Implantable medical systems and methods for use therewith that detect atrial capture and AV node capture responsive to his bundle pacing

ABSTRACT

Certain embodiments of the present technology described herein relate to detecting atrial oversensing in a His intracardiac electrogram (His IEGM), characterizing atrial oversensing, determining when atrial oversensing is likely to occur, and or reducing the chance of atrial oversensing occurring. Some such embodiments characterize and/or avoid atrial oversensing within a His IEGM. Other embodiments of the present technology described herein relate to determining whether atrial capture occurs in response to His bundle pacing (HBP). Still other embodiments of the present technology described herein relate to determining whether AV node capture occurs in response to HBP.

RELATED APPLICATION

The present application is related to commonly invented and commonlyassigned U.S. patent application Ser. No. 17/171,762 , filed the sameday as the present application, titled IMPLANTABLE MEDICAL SYSTEMS ANDMETHODS USED TO DETECT, CHARACTERIZE OR AVOID ATRIAL OVERSENSING WITHINA HIS IEGM, which is incorporated herein by reference.

FIELD

This disclosure relates generally to implantable cardiac stimulatingsystems and/or devices for use in providing His bundle pacing (HBP), andrelated methods. More specifically, the present disclosure is directedto cardiac stimulation systems and/or devices for providing HBP andassociated methods that perform, inter alia, atrial oversensing testing,atrial capture testing, and/or atrioventricular (AV) node capturetesting.

BACKGROUND

In a normal human heart, the sinus node, generally located near thejunction of the superior vena cava and the right atrium, constitutes theprimary natural pacemaker initiating rhythmic electrical excitation ofthe heart chambers. The cardiac impulse arising from the sinus node istransmitted to the two atrial chambers, causing a depolarization knownas a P-wave and the resulting atrial chamber contractions. Theexcitation pulse is further transmitted to and through the ventriclesvia the atrioventricular (AV) node and a ventricular conduction systemcomprised of the bundle of His (also referred to as the His bundle, ormore succinctly as the His), the left and right bundle branches, and thePurkinje fibers, causing depolarization and resulting contraction of theventricular chamber. The depolarization of the interventricular septumand ventricles is generally referred to as a QRS complex and is observedby measuring electrical activity of the heart, such as by recording anintracardiac electrocardiogram (IEGM).

The His bundle (aka the His, or the bundle of His) is a narrow clusterof cardiac muscle fibers that passes electrical impulses from the AVnode to the interventricular septum. It is anatomically located adjacentto the annulus of the tricuspid valve, inferior to or within themembranous septum. During normal functioning of the heart, the delaybetween excitation of the His bundle and a subsequent depolarization ofthe ventricles in response to the excitation is generally on the orderof approximately 30-50 milliseconds (ms) and the resulting QRS complexgenerally has a duration of approximately 70-100 ms.

Disruption of the natural pacemaking and conduction system of the heartas a result of aging or disease can be successfully treated byartificial cardiac pacing using implantable cardiac stimulation devices,including pacemakers and implantable defibrillators. Such devicesdeliver rhythmic electrical impulses at particular energies and rates orprovide other anti-arrhythmia therapies to the heart via electrodesimplanted in contact with the heart tissue. To the extent the electricalimpulses are sufficient to induce depolarization of the associated hearttissue, the heart tissue is said to be captured. The minimum electricalimpulse energy resulting in capture is generally referred to as thecapture threshold for the heart tissue.

In the majority of individuals, the most effective heartbeat istriggered by the patient's own natural pacing physiology. Implantablecardiac stimulation devices are intended to fill in when the naturalpacing functionality of the patient's heart fails or acts inefficiently(such as in cases of sinus arrest and symptomatic bradycardia,respectively) or when the heart's conduction system fails or actsinefficiently (such as in cases of third-degree and second-degree (i.e.,Mobitz II) AV blocks, respectively). In a large number of heart failurepatients, natural conduction through the AV node and the His bundle areintact and disruption of ventricular rhythm is the result of conductiondisorders residing in the left and/or right bundle branches.

Dilatation of the heart due to congestive heart failure (CHF) has beenassociated with delayed conduction through the ventricles. This delayedconduction leads to reduced hemodynamic efficiency of the failing heartbecause of the resulting poor synchronization of the heart chambers.

Direct stimulation of the His bundle has been found to providehemodynamic improvement for various patients including those sufferingfrom dilated cardiomyopathy but having otherwise normal ventricularactivation. Other examples of patients that may benefit from directstimulation of the His bundle include those with atrioventricularjunction (AVJ) ablation or third-degree AV block, which may requirepermanent ventricular pacing. Accordingly, the natural conductionsystem, when intact, can provide hemodynamically optimal depolarizationtiming of the heart chambers.

Permanent His bundle pacing (HBP) has become increasingly popular as analternative to right ventricular (RV) apical pacing for pacemakerpatients or biventricular (BV) pacing for cardiac resynchronizationtherapy (CRT). The close proximity of the His bundle to the basal-septalatrial myocardium, AV node, and basal-septal ventricular myocardiumpresents unique challenges to medical personnel that perform implants,especially those new to His implants. AV node capture or simultaneousHis and atrial capture may not be immediately apparent during an implantprocedure without performing additional testing. In cases withsuccessful His capture, the multi-signal components (one or more ofatrial, His, and ventricular signal component) in a His IEGM could alsodisrupt implantable device logic and impair its normal functionality.For example, a large atrial signal component, if present on the Hisbipolar or unipolar IEGM, can cause atrial oversensing and haveundesirable consequences. For example, where a device algorithm forautomated measurement of His capture type and threshold relies on abipolar and unipolar evoked response, such an algorithm may provideinaccurate results if atrial oversensing occurs. Additionally, a largeatrial signal component or unintended atrial and AV node capture maycause unreliable sensing of the HBP evoked response, thus rendering thealgorithm inaccurate.

BRIEF SUMMARY OF THE DISCLOSURE

Certain embodiments of the present technology described herein relate todetecting atrial oversensing in a His intracardiac electrogram (HisIEGM), characterizing atrial oversensing, determining when atrialoversensing is likely to occur, and or reducing the chance of atrialoversensing occurring. Other embodiments of the present technologydescribed herein relate to determining whether atrial capture occurs inresponse to His bundle pacing (HBP). Still other embodiments of thepresent technology described herein relate to determining whether AVnode capture occurs in response to HBP.

Certain methods of the present technology relate to methods for use withan implantable medical system including one or more electrodes that canbe used for sensing and pacing. One such method includes obtaining a HisIEGM sensed using at least one electrode implanted in or proximate to apatient's His bundle; sensing or pacing a right atrium of the patient tothereby sense or pace an atrial event; determining whether a portion ofthe His IEGM exceeds a specified sense threshold within a specifiedwindow that begins an atrioventricular delay (AVD) following the sensedor paced atrial event; and detecting atrial oversensing based on resultsof the determining whether a portion of the His IEGM exceeds thespecified sense threshold within the specified window. In accordancewith an embodiment, the specified window, which begins the AVD followingthe sensed or paced atrial event, comprises an evoked response window.In such an embodiments, the determining whether a portion of the HisIEGM exceeds the specified sense threshold within the specified windowincludes (at the AVD following the sensed or paced atrial event)triggering the evoked response window by delivering a subthresholdpacing pulse to a patient's His bundle using at least one electrode thatis implanted in or proximate to the patient's His bundle, thesubthreshold pacing pulse having energy below a capture thresholdassociated with the patient's His bundle and the right ventricular (RV)myocardium. The method can also include determining a first onsetinterval corresponding to a length of time between a beginning of thespecified window and when the portion of the His IEGM exceeds thespecified sense threshold within the specified window; sensing or pacingthe right atrium of the patient to thereby sense or pace a furtheratrial event; determining whether a portion of the His IEGM exceeds thespecified sense threshold within a further specified window that beginsat an extended AVD following the further sensed or paced atrial event,wherein the extended AVD is equal to the specified AVD plus an extensioninterval that is less than the first onset interval; determining asecond onset interval corresponding to a length of time between abeginning of the further specified window and when the portion of theHis IEGM within the further specified window exceeds the specified sensethreshold; determining whether the second onset interval is equal to thefirst onset interval minus the extension interval; and detecting atrialoversensing in response to determining that the second onset interval isequal to the first onset interval minus the extension interval. Themethod can also include preventing performance of His capture managementin response to detecting atrial oversensing, and after detecting atrialoversensing, at a later point in time that atrial oversensing is nolonger detected, enabling performance of the His capture management.

Certain embodiments of the present technology relate to a medical systemcomprising: one or more implantable electrodes that can be used forsensing and pacing a patient's His bundle; a sensing circuit configuredto sense a His IEGM using at least one said electrode that is implantedin or proximate to the patient's His bundle; a pulse generatorconfigured to selectively produce pacing pulses that are delivered tothe patient's His bundle using at least one said electrode that isimplanted in or proximate to the patient's His bundle; and a controller.In accordance with certain embodiments, the controller is configured to:determine whether a portion of the His IEGM exceeds a specified sensethreshold within a specified window that begins an AVD following thesensed or paced atrial event; and detect atrial oversensing based onresults of the determining whether a portion of the His IEGM exceeds thespecified sense threshold within the specified window. In certainembodiments, the specified window, which begins the AVD following thesensed or paced atrial event, comprises an evoked response window; andthe controller (in order to determine whether a portion of the His IEGMexceeds the specified sense threshold within the specified window thatbegins the AVD following the sensed or paced atrial event) is configuredto (at the AVD following the sensed or paced atrial event) trigger theevoked response window by causing delivery of a subthreshold pacingpulse to a patient's His bundle using at least one electrode that isimplanted in or proximate to the patient's His bundle, the subthresholdpacing pulse having energy below a capture threshold associated with thepatient's His bundle and the RV myocardium. Additional features and/orfunctions of the controller can be appreciated from the above portion ofthis summary, and the detailed description set forth below.

Another method of the present technology comprises: obtaining a His IEGMsensed using at least one electrode implanted in or proximate to apatient's His bundle; sensing or pacing a right atrium of the patient tothereby sense or pace an atrial event; determining whether a portion ofthe His IEGM exceeds a specified sense threshold within a specifiedwindow within an AVD following the sensed or paced atrial event; anddetecting an atrial signal component within the His IEGM based onresults of the determining whether a portion of the His IEGM exceeds thespecified sense threshold within the specified window within the AVD. Insuch an embodiment, detecting an atrial signal component within the HisIEGM is indicative of potential atrial oversensing. In certainembodiments, the AVD is long enough to allow for intrinsicatrioventricular conduction within the AVD; and the method is performedwhile the implantable medical system is in one of DDT or DDD mode. Inone embodiment, the method is performed while the implantable medicalsystem is in DDT mode, and the method further comprises triggeringventricular pacing in response to detecting a portion of the His IEGMexceeding the specified sense threshold within the AVD, or at the end ofthe AVD if no portion of the His IEGM exceeds the specified sensethreshold within the AVD.

In certain embodiments, in response to detecting an atrial signalcomponent within the His IEGM, the obtaining, pacing, and determiningare repeated one or more time(s) to confirm the detecting of an atrialsignal component within the His IEGM. In certain embodiments, inresponse to detecting an atrial signal component within the His IEGM, orconfirmation thereof, the method further comprises: determining anatrial event-to-threshold crossing interval corresponding to a length oftime between a paced or sensed atrial event and a respective crossing ofthe specified sense threshold; and specifying an atrial oversensingavoidance (AOA) period based on the atrial event-to-threshold crossinginterval, the AOA period corresponding to when atrial oversensing mayoccur following paced or sensed atrial events. A method can alsocomprise, after specifying the AOA period: determining that a portion ofthe His IEGM within the AOA period exceeds a specified sense threshold,detecting a peak amplitude of the portion of the His IEGM that exceedsthe specified sense threshold within the AOA period; detecting a peak ofa portion of the His IEGM, following the AOA period, that corresponds toa ventricular depolarization; determining a ratio of the peak amplitudewithin the AOA period to the peak amplitude following the AOA period;determining whether the determined ratio exceeds specified ratiothreshold; and determining that an atrial oversensing avoidancetechnique is to be used in response to determining that the determinedratio exceeds the specified ratio threshold. In accordance with anembodiment, after specifying the AOA period, and while the implantablemedical system is in DDD mode, the method also includes: sensing orpacing the right atrium of the patient to thereby sense or pace anatrial event; and determining whether a portion of the His IEGM exceedsa multi-level sense threshold within a specified window that beginsfollowing the sensed or paced atrial event; wherein the multi-levelsense threshold is greater during each said AOA period than followingeach said AOA period.

A medical system, according to an embodiment of the present technology,comprises: one or more implantable electrodes that can be used forsensing and pacing a patient's His bundle; a sensing circuit configuredto sense a His IEGM using at least one said electrode that is implantedin or proximate to the patient's His bundle; a pulse generatorconfigured to selectively produce pacing pulses that are delivered tothe patient's His bundle using at least one said electrode that isimplanted in or proximate to the patient's His bundle; and a controller.The controller is configured to: cause sensing or pacing of the rightatrium of the patient to thereby sense or pace an atrial event;determine whether a portion of the His IEGM exceeds a specified sensethreshold within a specified window within an AVD following the sensedor paced atrial event; and detect an atrial signal component within theHis IEGM based on whether it is determined that a portion of the HisIEGM exceeds the specified sense threshold within the specified windowwithin the AVD. In certain embodiments, the controller is alsoconfigured to: determine an atrial event-to-threshold crossing intervalcorresponding to a length of time between a paced or sensed atrial eventand a respective crossing of the specified sense threshold within thespecified window within the AVD; specify an atrial oversensing avoidance(AOA) period based on the atrial event-to-threshold crossing interval,the AOA period corresponding to when atrial oversensing may occurfollowing paced or sensed atrial events; detect a peak amplitude of aportion of the His IEGM that exceeds the specified sense thresholdwithin the AOA period; detect a peak of a portion of the His IEGM,following the AOA period, that corresponds to a ventriculardepolarization; determine a ratio of the peak amplitude within the AOAperiod to the peak amplitude following the AOA period; determine whetherthe determined ratio exceeds specified ratio threshold; and determinethat an atrial oversensing avoidance technique is to be used in responseto determining that the determined ratio exceeds the specified ratiothreshold. The controller can also be configured to: determine whether aportion of the His IEGM exceeds a multi-level sense threshold within aspecified window that begins following a sensed or paced atrial event;wherein the multi-level sense threshold is greater during each said AOAperiod than following each said AOA period.

Certain embodiments of the present technology relate to a method forperforming an atrial capture test that can be used to detect if and/orwhen atrial capture occurs in response to pacing a patient's His bundleusing at least one electrode that is implanted in or proximate to thepatient's His bundle. Such a method comprises: during a plurality ofcardiac cycles during which pacing of a patient's His bundle occursusing at least one electrode implanted in or proximate to a patient'sHis bundle, gradually decremented over time amplitudes of pacing pulsesthat are delivered to the patient's His bundle until loss of His or RVmyocardium capture occurs, such that the patient's His bundle is pacedat a plurality of different pacing pulse amplitudes; for each pacingpulse amplitude, of the different pacing pulse amplitudes used duringthe pacing of the patient's His bundle, determining a respectivestimulation-to-atrial sense (stim-to-AS) interval corresponding to alength of time between when a said His pacing pulse having the pacingpulse amplitude is delivered and when a respective atrial sensed eventoccurs; detecting how many increases to the stim-to-AS intervaloccurred, if any, in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs; and determining whether atrial capture occurred, duringthe pacing of the patient's His bundle, based on results of thedetecting how many increases to the stim-to-AS interval occurred, ifany. If one or more increases to the stim-to-AS interval are detected,the method also includes identifying a corresponding pacing pulseamplitude at which each of the one or more increases to the stim-to-ASinterval occurred, and the determining whether atrial capture occurredis also based on the corresponding pacing pulse amplitude at which atleast one of the one or more increases to the stim-to-AS intervaloccurred. The method can also include determining that atrial captureoccurred and that an atrial capture threshold is below a capturethreshold of the His bundle, if there were zero detected increases tothe stim-to-AS interval in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs. In accordance with certain embodiments, afterdetermining that atrial capture occurred, the method further comprises:determining an atrial capture threshold; and selecting a pacing pulseamplitude, at which to perform further pacing of the patient's Hisbundle, that is below the atrial capture threshold and above theamplitude at which loss of His or RV myocardium capture occurs.Additional details of this method are described below in the detaileddescription. The above summarized method can be used during an implantprocedure to help select a location for chronic implant of a lead and/orelectrode that is to be used for pacing of the patient's His bundle.

A medical system, according to an embodiment of the present technology,comprises: one or more implantable electrodes that can be used forsensing and pacing; a sensing circuit configured to sense a His IEGMusing at least one said electrode that is implanted in or proximate to apatient's His bundle; a pulse generator configured to selectivelyproduce pacing pulses that are delivered to the patient's His bundleusing at least one said electrode that is implanted in or proximate tothe patient's His bundle; and a controller. The controller is configuredto: cause gradual decrementing over time of amplitudes of pacing pulsesthat are delivered to the patient's His bundle until loss of His or RVmyocardium capture occurs, such that the patient's His bundle is pacedat a plurality of different pacing pulse amplitudes; for each pacingpulse amplitude, of the different pacing pulse amplitudes used duringthe pacing of the patient's His bundle, determine a respectivestim-to-AS interval corresponding to a length of time between when asaid His pacing pulse having the pacing pulse amplitude is delivered andwhen a respective atrial sensed event occurs; detect how many increasesto the stim-to-AS interval occurred, if any, in response to the pacingpulse amplitudes being gradually decremented over time until the loss ofHis or RV myocardium capture occurs; and determine whether atrialcapture occurred, during the pacing of the patient's His bundle, basedon results of the detecting how many increases to the stim-to-ASinterval occurred, if any. The controller can also be configured to:identify a corresponding pacing pulse amplitude at which each of the oneor more increases to the stim-to-AS interval occurred, if one or moreincreases to the stim-to-AS interval are detected; and determine whetheratrial capture occurred, during the pacing of the patient's His bundle,also based on the corresponding pacing pulse amplitude at which at leastone of the one or more increases to the stim-to-AS interval occurred.The controller can further be configured to: determine that atrialcapture occurred and that an atrial capture threshold is below a capturethreshold of the His bundle if there were zero detected increases to thestim-to-AS interval in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs. In accordance with certain embodiments, the controlleris also configured to: determine an atrial capture threshold if atrialcapture occurred; and select a pacing pulse amplitude, at which toperform further pacing of the patient's His bundle, that is below theatrial capture threshold and above the amplitude at which loss of His orRV myocardium capture occurs. Additional features and/or functions ofthe controller can be appreciated from the above portion of thissummary, and the detailed description set forth below.

Certain methods of the present technology relate to methods for use withan implantable medical system including one or more electrodes that canbe used for sensing and pacing. One such method includes obtaining a HisIEGM sensed using at least one electrode implanted in or proximate to apatient's His bundle; for each of a plurality of cardiac cycles duringwhich the His IEGM is obtained, sensing or pacing a right atrium of thepatient to thereby sense or pace an atrial event, pacing the patient'sHis bundle at a shortened AVD following the sensed or paced atrialevent, and determining whether a portion of the His IEGM exceeds aspecified sense threshold within a specified window that begins theshortened AVD following the sensed or paced atrial event. The methodalso includes determining whether AV node capture occurred based onresults of the determining whether a portion of the His IEGM exceeds thespecified sense threshold within the specified window. In accordancewith certain embodiments, the specified window, which begins theshortened AVD following the sensed or paced atrial event, comprises anevoked response window; and the pacing the patient's His bundle at theshortened AVD following the sensed or paced atrial event comprises, (atthe shortened AVD following the sensed or paced atrial event) triggeringthe evoked response window by delivering a pacing pulse to a patient'sHis bundle using at least one electrode that is implanted in orproximate to the patient's His bundle, the pacing pulse having energyabove a capture threshold associated with the patient's His bundle orthe RV myocardium. The method can include determining that AV nodecapture did occur, in response to determining that a portion of the HisIEGM did not exceed the specified sense threshold within the specifiedwindow that begins the shortened AVD following the sensed or pacedatrial event. In accordance with certain embodiments, in response todetermining that a portion of the His IEGM did exceed the specifiedsense threshold within the specified window that begins the shortenedAVD following the sensed or paced atrial event, then determining thatone of AV node capture or His bundle capture occurred, anddistinguishing between AV node capture and His bundle capture. Inaccordance with certain embodiments, the distinguishing between AV nodecapture and His bundle capture is achieved by performing the following:during a further plurality of cardiac cycles during which pacing of thepatient's His bundle occurs using the at least one electrode implantedin or proximate to a patient's His bundle, gradually decrementing overtime a His bundle cycle length pacing interval, determining whetherstimulation-to-onset intervals progressively increased in response tothe gradually decrementing over time the His bundle cycle length pacinginterval, and determining that AV node capture occurred, in response todetermining that the stimulation-to-onset intervals progressivelyincreased in response to the gradually decrementing over time the Hisbundle cycle length pacing interval. If the stimulation-to-onsetintervals did not progressively increase in response to the graduallydecrementing over time the His bundle cycle length pacing interval, thenit would have been determined that His bundle capture occurred withoutAV node capture. The aforementioned method can be used during an implantprocedure to help select a location for chronic implant of a lead and/orelectrode that is to be used for pacing of the patient's His bundle, andthe lead and/or electrode can be repositioned if AV node capture isdetected.

A medical system, according to an embodiment of the present technology,comprises: one or more implantable electrodes that can be used forsensing and pacing; a sensing circuit configured to sense a His IEGMusing at least one said electrode that is implanted in or proximate to apatient's His bundle; a pulse generator configured to selectivelyproduce pacing pulses that are delivered to the patient's His bundleusing at least one said electrode that is implanted in or proximate tothe patient's His bundle; and a controller. The controller is configuredto: cause sensing or pacing of a right atrium of the patient to therebysense or pace an atrial event for each of a plurality of cardiac cyclesduring which an IEGM is being sensed using at least one electrodeimplanted in or proximate to a patient's His bundle. The controller isalso configured to cause pacing of the patient's His bundle at ashortened AVD following the sensed or paced atrial event; determinewhether a portion of the His IEGM exceeds a specified sense thresholdwithin a specified window that begins the shortened AVD following thesensed or paced atrial event; and determine whether AV node captureoccurred based on whether a portion of the His IEGM exceeds thespecified sense threshold within the specified window. In accordancewith certain embodiments, the controller is configured to determine thatAV node capture did occur, in response to determining that a portion ofthe His IEGM did not exceed the specified sense threshold within thespecified window that begins the shortened AVD following the sensed orpaced atrial event. In accordance with certain embodiments, thecontroller is configured to: determine that one of AV node capture orHis bundle capture occurred in response to determining that a portion ofthe His IEGM did exceed the specified sense threshold within thespecified window that begins the shortened AVD following the sensed orpaced atrial event, and distinguish between AV node capture and Hisbundle capture. The controller can be configured to distinguish betweenAV node capture and His bundle capture by performing the following:during a further plurality of cardiac cycles during which pacing of thepatient's His bundle occurs using the at least one electrode implantedin or proximate to a patient's His bundle, causing a graduallydecrementing over time a His bundle cycle length pacing interval;determine whether stimulation-to-onset intervals progressively increasedin response to the gradually decrementing over time the His bundle cyclelength pacing interval; and determine that AV node capture occurred, inresponse to determining that the stimulation-to-onset intervalsprogressively increased in response to the gradually decrementing overtime the His bundle cycle length pacing interval. The controller canalso be configured to determine that His bundle capture occurred withoutAV node capture, in response to determining that thestimulation-to-onset intervals did not progressively increase inresponse to the gradually decrementing over time the His bundle cyclelength pacing interval.

This summary is not intended to be a complete description of theembodiments of the present technology. Other features and advantages ofthe embodiments of the present technology will appear from the followingdescription in which the preferred embodiments have been set forth indetail, in conjunction with the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features of the present disclosure and the manner ofattaining them will be described in greater detail with reference to thefollowing description, claims, and drawings, wherein reference numeralsare reused, where appropriate, to indicate a correspondence between thereferenced items, and wherein:

FIG. 1 is a simplified, partly cutaway view illustrating an implantablestimulation device in electrical communication with multiple leads,including a His bundle lead, implanted into a patient's heart fordelivering multi-chamber stimulation and shock therapy.

FIG. 2 is a simplified, partly cutaway view illustrating an alternativedesign of an implantable stimulation device, shown implanted into theright chambers of the patient's heart for delivering dual-chamberstimulation and shock therapy.

FIG. 3 is a functional block diagram of the multi-chamber implantablestimulation device of FIG. 1 or 2 , illustrating the basic elements thatprovide pacing stimulation, cardioversion, and defibrillation in four(or less) chambers of the heart.

FIG. 4 is a partly fragmentary illustration of the distal end of the Hisbundle lead for use with the stimulation device of FIG. 3 , depicting atip electrode with an active fixation device and a non-traumaticconductive surface, and a ring electrode.

FIG. 5 is a high level flow diagram that is used to describe certainmethods for determining whether or not atrial oversensing is detectedwithin a His IEGM.

FIG. 6 illustrates example His bipolar and His unipolar IEGMs that areused to explain in more detail how atrial oversensing may be detectedusing the methods described with reference to the flow diagram of FIG. 5.

FIGS. 7A and 7B, which can be collectively referred to as FIG. 7 ,include a high level flow diagram that is used to describe methods fordetermining whether or not atrial oversensing may occur, and if so, howto characterize potential atrial oversensing and/or reduce thelikelihood of atrial oversensing.

FIG. 8 illustrates a multi-level sense threshold which can be used toavoid atrial oversensing between the time of an atrial sensed event (AS)or atrial paced event (AP) and a following ventricular depolarizationrepresented in a His IEGM, in accordance with certain embodiments of thepresent technology.

FIG. 9A includes a table that summarizes stim-to-onset intervals ofpatient's with and without oversensing, which table can be used tospecify the length of the specified window used with the atrialoversensing test summarized with reference to FIGS. 5 and 6 .

FIG. 9B includes a table that summarizes AS/AP to onset intervals ofpatient's with and without oversensing, which table can be used tospecify the length of the specified window used with the atrialoversensing test summarized with reference to FIG. 7 .

FIGS. 10A and 10B, which can be collectively referred to as FIG. 10 ,includes a high level flow diagram that is used to describe methods forperforming an atrial capture test, in accordance with certainembodiments of the present technology, wherein such a test can be usedto detect if and/or when atrial capture occurs in response to HBP.

FIGS. 11A-11G each include an example atrial bipolar IEGM and an exampleHis bipolar IEGM that are used to show how the atrial capture test,which is described with reference to the high level flow diagram of FIG.10 , can be used to detect whether atrial capture occurs in response toHBP, as well as to provide other types of determinations.

FIG. 12 includes a high level flow diagram that is used to describecertain methods for determining whether or not AV node capture occurs inresponse to HBP.

FIGS. 13A and 13B, which can be collectively referred to as FIG. 13 ,shows examples His IEGMs that are used to explain how the methodsdescribed with reference to the flow diagram of FIG. 12 can be used todetermine whether or not AV node capture occurs in response to HBP.

DETAILED DESCRIPTION

The present disclosure is directed to various aspects of stimulationdevices and corresponding methods related to His bundle pacing (HBP).Among other things, the present disclosure provides methods and devicesfor performing atrial oversensing, atrial capture, and AV node capturetesting. Aspects of the present disclosure may be implemented in anysuitable stimulation device including, but not limited to, implantabledual chamber and multi-chamber cardiac stimulation devices as well asexternal programming units for such stimulation devices. For example,the present disclosure may be implemented in multi-chamber cardiacstimulation device such as the stimulation device 100 depicted in FIG. 1.

Certain cardiac pacemakers and defibrillators incorporate a pacing leadin the right ventricle and may also include a second lead in the rightatrium. High-burden right ventricle apical pacing may contribute to thedevelopment of pacing-induced cardiomyopathy and symptoms associatedwith heart failure (HF). Several pathophysiologic mechanisms have beenimplicated in the development of pacing-induced HF, each of which likelystems from non-physiological electrical and mechanical activationpatterns produced by right ventricle pacing. HBP has been shown torestore physiological activation patterns by utilizing a patient'sintrinsic conduction system, even in the presence of bundle branchblock. HBP has also been shown to provide significant QRS narrowing,with improved ejection fraction.

Another possible clinical application of HBP is cardiacresynchronization therapy (CRT). Conventional CRT systems include pacingfrom both a right ventricular and a left ventricular lead, and have beenshown to be most effective for patients exhibiting a wide QRS complexand left bundle branch block. HBP has also been shown to be effective atnarrowing the QRS complex in patients with left bundle branch block,likely due to restoration of conduction through the Purkinje fibers,which include right and left bundle fibers that are longitudinallydissociated. Therefore, what is thought of as left bundle branch block,can be a result of a proximal blockage within the His bundle thateventually branches to the left bundle. By pacing the His bundle distalto the blockage, a normalized QRS complex can be achieved in somepatients. Theoretically, this pacing mode may provide even betterresults than known CRT treatments, as activation propagates rapidlythrough natural conduction pathways.

Depending on electrode position, pacing output, patient physiology, andother factors, pacing impulses delivered to the His bundle may result incapture of different cardiac tissue. As used herein, the term “capture”refers to when a pacing impulse has sufficient energy to depolarizecardiac tissue, thereby causing the depolarized cardiac tissue tocontract. In the context of HBP, pacing of the His bundle will generallyresult in one of four capture scenarios: non-selective (NS) His bundlecapture, selective (S) His bundle capture, myocardium-only (Myo)capture, or loss of capture (LOC) (aka non-capture). Non-selectivecapture refers to when a pacing impulse results in capture of both theHis bundle and the local myocardium surrounding the His bundle. Becauseof the simultaneous depolarization of the His bundle and myocardium,non-selective His bundle capture generally results in a combined orcondensed electrical response as compared to normal heart activity inwhich the His bundle and myocardium are depolarized sequentially.Accordingly, non-selective His bundle capture may be characterized by ashortened delay between application of the pacing impulse andventricular depolarization (e.g., on the order of 20 ms) because themyocardial depolarization propagates immediately without exclusivelytraveling through the His-Purkinje system. Nevertheless, because the Hisbundle is stimulated and captured, the QRS duration is similar to thenative QRS duration but may be slightly longer due to the myocardialexcitation (e.g., 70-120 ms). In contrast, selective His bundle capturerefers to exclusive capture of the His bundle without depolarization ofthe surrounding myocardial tissue. With selective His bundle capture,the stimulus to ventricular depolarization interval is virtually thesame as the native delay between His bundle activation and subsequentventricular depolarization and the QRS duration is essentially identicalto the native QRS duration. In myocardium-only capture, the tissuesurrounding the His bundle is captured without capturing the His bundleitself, resulting in slow or delayed signal conduction and activation.Finally, loss of capture generally refers to circumstances in which theapplied stimulus is insufficient or otherwise unable to elicit aresponse. In such cases, backup pacing may be applied. For patients withbranch bundle block or similar conduction disorders, the foregoingcapture types may be further characterized by whether they result incorrection of the conduction disorder. For example, a pacing impulse mayresult in any of non-selective His bundle capture with correction,non-selective His bundle capture without correction, selective Hisbundle capture with correction, or selective His bundle capture withoutcorrection.

While both selective and non-selective His bundle capture may be used toimprove cardiac function, selective His bundle capture is generallypreferred as the corresponding response more closely approximatesnatural heart function. However, due to the complexity and dynamicnature of certain cardiomyopathies and cardiac anatomies, selective Hisbundle capture may not be possible or, if possible at one time, may nolonger be possible as a patient's condition changes over time. Moreover,a patient's condition may also progress such that His bundle capture(whether selective or non-selective) may become unavailable and, as aresult, direct ventricular pacing may be required.

In light of the foregoing, methods and apparatuses directed tooptimizing HBP have been developed, examples of which are disclosed incommonly assigned U.S. Provisional Patent Application No. 62/948,047,titled AUTOMATIC PACING IMPULSE CALIBRATION USING PACING RESPONSETRANSITIONS filed Dec. 13, 2019, which is incorporated herein byreference. More specifically, the aforementioned patent applicationdescribes stimulation devices capable of HBP and processes that may beimplemented by such stimulation devices to initialize device settings.To do so, stimulation devices or a programming unit in communicationwith the stimulation device executes a capture threshold test in whichresponse data is collected for a range of pacing impulse energies (e.g.,a range of pacing impulse voltages, pacing impulse pulse widths, orcombinations thereof). In certain implementations, the response data mayinclude unipolar, bipolar, or both unipolar and bipolar responses (e.g.,IEGMs) recorded and stored by the stimulation device or programmingunit. Transitions between capture types are then identified by analyzingchanges in response characteristics for the various pacing impulseenergy settings that were tested. Based on the number of observedtransitions, the nature of the changes indicating the transitions (e.g.,how the particular response characteristics change), an initial capturetype, and/or other similar factors, the capture pacing impulse energiesmay then be assigned a capture type. The stimulation device orprogramming unit may then identify capture thresholds based on thepacing impulse energies at which transitions between different capturetypes occur and calibrate or adjust stimulation device settings to thebest available pacing impulse energy (e.g., the lowest energy (thelowest voltage, pulse width, or combination thereof) for which HBPcapture is achieved) according to the assigned capture types and/oridentified capture thresholds. By relying on response data obtained fromthe patient, the settings of the stimulation device are specificallytailored to the individual patient and, as a result, improve both pacingreliability and overall life and function of the stimulation device.

As noted above in the Background, the close proximity of the His bundleto the basal-septal atrial myocardium, AV node, and basal-septalventricular myocardium presents unique challenges to medical personnelthat perform implants, especially those new to His implants. AV nodecapture or simultaneous His and atrial capture may not be immediatelyapparent during an implant procedure without performing additionaltesting. In cases with successful His capture, the multi-signalcomponents (one or more of atrial, His, and ventricular signal) in a HisIEGM could also disrupt implantable device logic and impair its normalfunctionality. For example, a large atrial signal component, if presenton the His bipolar or unipolar IEGM, can cause atrial oversensing andhave undesirable consequences. For example, where a device algorithm forautomated measurement of His capture type and threshold relies on abipolar and unipolar evoked response, such an algorithm may provideinaccurate results if atrial oversensing occurs. Additionally, a largeatrial signal component or unintended atrial and AV node capture maycause unreliable sensing of the HBP evoked response, thus rendering thealgorithm inaccurate. Certain embodiments of the present disclosure arerelated to atrial oversensing testing, atrial capture testing, and AVnode testing. As will be appreciated by the description below, theresults of such testing can be used in various different manners toimprove the use of HBP and/or to improve an implant procedure where thedesire it to implant a lead and/or electrode in or proximate to the Hisbundle.

Before providing additional details of the embodiments of the presetdisclosure, FIGS. 1-4 are first used to generally describe thecomponents and functionality of example stimulation devices that may beused to implement aspects of the present disclosure. It should beappreciated that FIGS. 1-4 should be understood to be representativeonly and are therefore non-limiting. Rather, the methods and techniquesdescribed herein may be implemented using any suitable stimulationsystem/device capable of pacing the His bundle and obtaining andanalyzing corresponding response data to such pacing activities. Forexample and unless otherwise specifically noted, stimulation devices inaccordance with the present disclosure may include any number of leadsconfigured to provide stimulation and/or pacing as described herein andmay include either unipolar or bipolar leads. Moreover, it shouldfurther be understood that the methods disclosed herein may also beperformed, at least in part, by an external testing or programming unitcapable of receiving and transmitting data from an implantablestimulation device. Such data may include, without limitation, responsedata measured by the stimulation device and transmitted to the externalunit and configuration data transmitted from the external unit to thestimulation device to configure the stimulation device. Further, itshould be noted that instead of using a His bundle lead to deliver HBPpulses, and to sense His IEGMs, it would also be possible to use aleadless cardiac pacemaker (LCP) that is implanted at least partiallywithin or adjacent to the His bundle to deliver HBP pulse, and/or senseHis IEGMs, and more generally, to perform or otherwise implement theembodiments described herein.

Referring to FIG. 1 , a stimulation device 110 is shown in electricalcommunication with a patient's heart 112 by way of four leads, 120, 121,124, and 130 and is therefore suitable for delivering multi-chamberstimulation and shock therapy. To sense atrial cardiac signals and toprovide right atrial chamber stimulation therapy, the stimulation device110 is coupled to an implantable right atrial lead 120 having at leastan atrial tip electrode 122, which typically is implanted in thepatient's right atrial appendage or atrial septum.

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, the stimulation device 110 is coupled to a“coronary sinus” lead 24 designed for placement in the “coronary sinusregion” via the coronary sinus ostium for positioning a distal electrodewithin the coronary veins overlying the left ventricle and/or additionalelectrode(s) adjacent to the left atrium. As used herein, the phrase“coronary sinus region” refers to the vasculature of the left ventricle,including any portion of the coronary sinus, great cardiac vein, leftmarginal vein, left posterior ventricular vein, middle cardiac vein,and/or small cardiac vein or any other cardiac vein accessible by thecoronary sinus which overlies the left ventricle.

Accordingly, an exemplary coronary sinus lead 124 is designed to receiveatrial and ventricular cardiac signals and to deliver left ventricularpacing therapy using at least a left ventricular tip electrode 126, leftatrial pacing therapy using at least a left atrial ring electrode 127,and shocking therapy using at least a left atrial coil electrode 128. Inanother embodiment, an additional electrode for providing leftventricular defibrillation shocking therapy may be included in theportion of the lead overlying the left ventricle, adjacent to the ringelectrode 125.

The stimulation device 110 illustrated in FIG. 1 is generally configuredas an implantable cardioverter-defibrillator (ICD) and generallyincludes functionality for pacing, sensing, and providing defibrillationto a patient heart. It should be appreciated however, that the ICDillustrated in FIG. 1 is just one example stimulation device that mayimplement aspects of the present disclosure. Other configurations andtypes of implantable stimulation devices incorporating aspects of thepresent disclosure are also contemplated. For example and withoutlimitation, in at least one implementation, the stimulation device 110of FIG. 1 may instead be configured as a pacemaker withoutdefibrillation functionality and, in particular, a pacemaker configuredto provide cardiac resynchronization therapy (CRT). In suchimplementations, some or all of the defibrillation coils illustrated onthe various leads of FIG. 1 and their associated circuitry within thestimulation device 110 may be omitted. It should also be appreciatedthat the specific configuration of leads and placement of leadsillustrated in FIG. 1 is intended merely as an example and otherconfigurations are possible. For example, in one specificimplementation, the coronary sinus lead 124 may instead be replaced witha left ventricle lead that extends and is implanted within the leftventricle for pacing and/or sensing of the left ventricle. Moregenerally, implementations of the present disclosure are generallyapplicable to any suitable stimulation devices currently known or laterdeveloped that provide His bundle pacing.

The stimulation device 110 is also shown in electrical communicationwith the patient's heart 112 by way of an implantable right ventricularlead 130 having, in this embodiment, a right ventricular tip electrode132, a right ventricular ring electrode 134, a right ventricular coilelectrode 136, and a superior vena cava (SVC) coil electrode 138.Typically, the right ventricular lead 130 is transvenously inserted intothe heart 112 so as to place the right ventricular tip electrode 132 inthe right ventricular apex so that the right ventricular coil electrode136 will be positioned in the right ventricle and the SVC coil electrode138 will be positioned in the superior vena cava. Accordingly, the rightventricular lead 130 is capable of receiving cardiac signals anddelivering stimulation in the form of pacing and shock therapy to theright ventricle.

The stimulation device 110 is further connected to a His bundle lead 121having a His tip electrode 116, such as a helical active fixationdevice, and a His ring electrode 119 located proximal from the His tipelectrode 116. In certain implementations, the His ring electrode 119 islocated approximately 10 mm proximal the His tip electrode 116. The Hisbundle lead 121 may be transvenously inserted into the heart 112 so thatthe His tip electrode 116 is positioned in the tissue of the His bundle.Accordingly, the His bundle lead 121 is capable of receivingdepolarization signals propagated in the His bundle and exiting thePurkinje fibers to the myocardium or delivering stimulation to the Hisbundle, creating a depolarization that can be propagated through thelower conductive pathways of the right and left ventricles (i.e., theright and left bundle branches and Purkinje fibers). The His bundle lead121 will be described in greater detail below in conjunction with FIG. 4.

An alternative embodiment of the present disclosure is shown in FIG. 2in which a dual chamber stimulation device 210 is in communication withone atrium, one ventricle, and the His bundle. Though not explicitlyillustrated in FIG. 2 , a right atrial lead 120 (shown in FIG. 1 ) canbe optionally included. In such implementations, the stimulation device210 maintains communication with the right atrium of the heart 112 via aright atrial lead 220 having at least an atrial tip electrode 222 and anatrial ring electrode 223 (which may be implanted in the patient's rightatrial appendage as described earlier in connection with FIG. 1 ), andan SVC coil electrode 239

A His bundle lead 221, having a His tip electrode 216 and a His ringelectrode 219, is positioned such that the His tip electrode 216 isproximate the His bundle tissue. The stimulation device 210 is shown inFIG. 2 in electrical communication with the patient's heart 112 by wayof a right ventricular lead 230 including a right ventricular tipelectrode 232, a right ventricular ring electrode 234, and a rightventricular coil electrode 236.

Referring now to FIG. 3 , there is illustrated a simplified blockdiagram of the multi-chamber implantable stimulation device 110 of FIG.1 (or 210 of FIG. 2 ), which is capable of treating both fast and slowarrhythmias with stimulation therapy, including cardioversion,defibrillation, and pacing stimulation. While a particular multi-chamberdevice is shown, this is for illustration purposes only, and one ofskill in the art could readily duplicate, eliminate or disable theappropriate circuitry in any desired combination to provide a devicecapable of treating the appropriate chamber(s) with cardioversion,defibrillation and pacing stimulation.

The housing 340 for the stimulation device 110 or 210, shownschematically in FIG. 3 , is often referred to as the “can”, “case” or“case electrode” and may be programmably selected to act as the returnelectrode for all “unipolar” modes. The housing 340 may further be usedas a return electrode alone or in combination with one or more of thecoil electrodes 128, 136, and 138 (shown in FIG. 1 ), or 236 and 239(shown in FIG. 2 ) for shocking purposes. The housing 340 furtherincludes a connector (not shown) having a plurality of terminals 342,344, 346, 348, 350-52, 354, 356, and 358 (shown schematically and, forconvenience, next to the names of the electrodes to which they areconnected). As such, to achieve right atrial sensing and pacing, theconnector includes at least a right atrial tip terminal (AR TIP) 342adapted for connection to the atrial tip electrode 222 (shown in FIG. 2).

To achieve left chamber sensing, pacing, and defibrillation (inapplications in which the stimulation device 110 or 210 is an ICD), theconnector includes at least a left ventricular tip terminal (VL TIP)344, a left atrial ring terminal (AL RING) 346, and a left atrialshocking terminal (AL COIL) 348, which are adapted for connection to theleft ventricular tip electrode 126, the left atrial ring electrode 127,and the left atrial coil electrode 128, respectively (each shown in FIG.1 ).

To support right chamber sensing, pacing and shocking, the connectorfurther includes a right ventricular tip terminal (VR TIP) 352, a rightventricular ring terminal (VR RING) 354, a right ventricular shockingterminal (RV COIL) 356, and an SVC shocking terminal (SVC COIL) 358,which are adapted for connection to the right ventricular tip electrode132, right ventricular ring electrode 134, the right ventricular coilelectrode 136, and the SVC coil electrode 138, respectively (each shownin FIG. 1 ).

To achieve His bundle sensing, or sensing and stimulation, the connectorfurther includes a His bundle lead tip terminal 350 and a His bundlelead ring terminal 351 which are adapted for connection to the His tipelectrode 116 and the His ring electrode 119, respectively (each shownin FIG. 1 ).

At the core of the stimulation device 110 or 210 is a programmablemicrocontroller 360 which controls the various modes of stimulationtherapy. The microcontroller 360 includes a microprocessor, orequivalent control circuitry, designed specifically for controlling thedelivery of stimulation therapy and may further include RAM or ROMmemory, logic and timing circuitry, state machine circuitry, and I/Ocircuitry. Typically, the microcontroller 360 includes the ability toprocess or monitor input signals (data) as controlled by a program codestored in a designated block of memory. The details of the design andoperation of the microcontroller 360 are not critical to the presentdisclosure. Rather, any suitable microcontroller 360 may be used thatcarries out the functions described herein.

As shown in FIG. 3 , an atrial pulse generator 370, a ventricular pulsegenerator 372, and a HBP pulse generator 399 generate pacing stimulationpulses for delivery by the right atrial lead 120, the right ventricularlead 130, the coronary sinus lead 124, and/or the His bundle lead 121(or 221) via an electrode configuration switch 374. As previously noted,in certain applications, the coronary sinus lead 124 may instead besubstituted with a left ventricle lead. It is understood that in orderto provide stimulation therapy in each of the chambers of the heartand/or to specific structures of the heart (e.g., the His bundle), theatrial, ventricular, and HBP pulse generators 370, 372, 399 may includededicated, independent pulse generators, multiplexed pulse generators,or shared pulse generators. The pulse generators 370, 372, 399 arecontrolled by the microcontroller 360 via appropriate control signals376, 378, 397, respectively, to trigger or inhibit the stimulationpulses. As used herein, the shape of the stimulation pulses is notlimited to an exact square or rectangular shape, but may assume any oneof a plurality of shapes which is adequate for the delivery of an energypulse, packet, or stimulus.

The microcontroller 360 further includes timing control circuitry 379which is used to control the timing of such stimulation pulses (e.g.,pacing rate) as well as to keep track of the timing of refractoryperiods, blanking intervals, noise detection windows, evoked responsewindows, alert intervals, marker channel timing, etc., which is wellknown in the art.

According to one embodiment of the present disclosure, timing controlcircuitry 379 also controls the onset and duration of a His signalsensing window during which a depolarization signal conducted throughthe AV node to the His bundle can be detected. Timing control circuitry379 also controls a timing delay provided after a detected His signaldetection, prior to the delivery of a right and/or left ventricularstimulation pulse.

The switch 374 includes a plurality of switches for connecting thedesired electrodes to the appropriate I/O circuits, thereby providingcomplete electrode programmability. Accordingly, the switch 374, inresponse to a control signal 380 from the microcontroller 360,determines the polarity of the stimulation pulses (e.g., unipolar,bipolar, cross-chamber, etc.) by selectively closing the appropriatecombination of switches (not shown) as is known in the art.

Atrial sensing circuits 382 and ventricular sensing circuits 384 mayalso be selectively coupled to the right atrial lead 320, coronary sinuslead 324 (or left ventricle lead), and the right ventricular lead 330,through the switch 374 for detecting the presence of cardiac activity ineach of the four chambers of the heart. Accordingly, the atrial (ATR.SENSE) and ventricular (VTR. SENSE) sensing circuits 382, 384 mayinclude dedicated sense amplifiers, multiplexed amplifiers, or sharedamplifiers. The switch 374 determines the “sensing polarity” of thecardiac signal by selectively closing the appropriate switches, as isalso known in the art. In this way, the clinician may program thesensing polarity independent of the stimulation polarity.

According to one implementation of the present disclosure, a His sensingcircuit 383 is selectively coupled to the His bundle lead 121 (shown inFIG. 1 ) or 221 (shown in FIG. 2 ) for detecting the presence of aconducted depolarization arising in the atria and conducted through theHis bundle via the AV node. As used herein, each of the atrial sensingcircuit 382, the ventricular sensing circuit 384, and the His sensingcircuit 383, includes a discriminator, which is a circuit that sensesand can indicate or discriminate the origin of a cardiac signal in eachof the cardiac chambers.

As illustrated in FIG. 3 , the His sensing circuit 383 is shown as adedicated circuit within the stimulation device 110 or 210. However, itshould be appreciated that in certain implementations, His-relatedfunctionality may instead be provided by repurposing other pacing andsensing channels and circuitry of the stimulation device 110 or 210. Forexample, the stimulation device 110 or 210 may be reprogrammed such thata pacing channel, a sensing channel, and associated circuitry initiallyprogrammed for use in sensing and pacing one of the atria or ventriclesmay instead be reconfigured to pace and sense the His bundle.

Each sensing circuit 382-384 preferably employs one or more low power,precision amplifiers with programmable gain and/or automatic gaincontrol, bandpass filtering, and a threshold detection circuit toselectively sense the cardiac signal of interest. The automatic gaincontrol enables the device 110 or 210 to deal effectively with thedifficult problem of sensing the low amplitude signal characteristics ofatrial or ventricular fibrillation.

The outputs of the sensing circuits 382-384 are connected to themicrocontroller 360 which, in turn, is able to trigger or inhibit theatrial and ventricular pulse generators 370, 372, respectively, in ademand fashion in response to the absence or presence of cardiacactivity in the appropriate chambers of the heart.

The atrial and ventricular sensing circuits 382, 384, in turn, receivecontrol signals over signal lines 386, 388, from the microcontroller 360for purposes of controlling the gain, threshold, polarization chargeremoval circuitry (not shown), and the timing of any blocking circuitry(not shown) coupled to the inputs of the sensing circuits 382, 384.

Similarly, the output of the His sensing circuit 383 is connected to themicrocontroller 360 which, in turn, is able to trigger or inhibit theHBP pulse generator 399 in a demand fashion in response to the absenceor presence of cardiac activity associated with the His bundle. The Hissensing circuit 383 may also receive control signals from themicrocontroller 360 for purposes of controlling gain, threshold,polarization charge removal circuitry, and the timing of any blockingcircuitry coupled to the inputs of the His sensing circuit 383.

As described below in further detail certain aspects of controlling orconfiguring the HBP pulse generator 399 may also be based onmeasurements related to activity of other structures/chambers of theheart. So, for example and without limitation, the HBP pulse generator399 may also be triggered, inhibited, calibrated, or configured based onoutputs from the atrial and ventricular sensing circuits 382-384 or anyother similar sensing circuit adapted to measure electrical activity ofthe heart.

For arrhythmia detection, the stimulation device 110 or 210 includes anarrhythmia detector 377 that utilizes the atrial and ventricular sensingcircuits 382, 384, to sense cardiac signals to determine whether arhythm is physiologic or pathologic. As used herein “sensing” isreserved for the noting of an electrical signal, and “detection” is theprocessing of these sensed signals and noting the presence of anarrhythmia. The timing intervals between sensed events (e.g., P-waves,R-waves, and depolarization signals associated with fibrillation) arethen classified by the microcontroller 360 by comparing them to apredefined rate zone limit (i.e., bradycardia, normal, low rate VT, highrate VT, and fibrillation rate zones) and various other characteristics(e.g., sudden onset, stability, physiologic sensors, and morphology,etc.) in order to determine the type of remedial therapy that is needed(e.g., bradycardia pacing, anti-tachycardia pacing, cardioversion shocksor defibrillation shocks, collectively referred to as “tiered therapy”).

Cardiac signals are also applied to the inputs of an analog-to-digital(A/D) data acquisition system 390 represented by an A/D converter. Thedata acquisition system 390 is configured to acquire intracardiacelectrogram signals, convert the raw analog data into a digital signal,and store the digital signals for later processing and/or telemetrictransmission to an external device 302. The data acquisition system 390is coupled to the right atrial lead 120, the His bundle lead 121 (or221), the coronary sinus lead 124, and the right ventricular lead 130(or 230) through the switch 374 to sample cardiac signals across anypair of desired electrodes.

In one embodiment, the data acquisition system 390 is coupled tomicrocontroller 360, or to other detection circuitry, for detecting adesired feature of the His bundle signal. In one embodiment, an averager365 is used to determine a sliding average of the His bundle signalduring a His signal sensing window using known or available signalaveraging techniques.

Advantageously, the data acquisition system 390 may be coupled to themicrocontroller 360, or other detection circuitry, for detecting anevoked response from the heart 112 in response to an applied stimulus,thereby aiding in the detection of capture. The microcontroller 360detects a depolarization signal during a window following a stimulationpulse, the presence of which indicates that capture has occurred. Themicrocontroller 360 enables capture detection by triggering theventricular pulse generator 372 to generate a stimulation pulse,starting a capture detection window using the timing control circuitry379 within the microcontroller 360, and enabling the data acquisitionsystem 390 via control signal 392 to sample the cardiac signal thatfalls in the capture detection window and, based on the amplitude,determines if capture has occurred.

Capture detection may occur on a beat-by-beat basis or on a sampledbasis. Preferably, a capture threshold search is performed at least oncea day during at least the acute phase (e.g., the first 30 days followingdevice implant) and less frequently thereafter. A capture thresholdsearch would begin at a desired starting point (either a high energylevel or the level at which capture is currently occurring) and decreasethe energy level until capture is lost. The minimum energy at whichcapture is consistently obtained is known as the capture threshold.Thereafter, a safety margin can be automatically or programmably addedto the capture threshold.

Capture detection and threshold testing may also be performed forpurposes of His bundle pacing. Processes for performing capturethreshold testing for His bundle pacing and configuring the stimulationdevice 110 or 210 based on the results of such testing are described inmore detail below.

The microcontroller 360 is further coupled to a memory 394 by a suitabledata/address bus 396, wherein the programmable operating parameters usedby the microcontroller 360 are stored and modified, as required, inorder to customize the operation of the stimulation device 310 to suitthe needs of a particular patient. Such operating parameters define, forexample, pacing pulse amplitude, pulse duration, electrode polarity,rate, sensitivity, automatic features, arrhythmia detection criteria,and the amplitude, waveshape and vector of each shocking pulse to bedelivered to the patient's heart 112 within each respective tier oftherapy.

Advantageously, the operating parameters of the implantable device 110may be non-invasively programmed into the memory 394 through a telemetrycircuit 300 in telemetric communication with the external device 302,such as a programmer, transtelephonic transceiver, or a diagnosticsystem analyzer. The telemetry circuit 300 is activated by themicrocontroller 360 by a control signal 306. The telemetry circuit 300advantageously allows intracardiac electrograms and status informationrelating to the operation of the device 110 or 210 (as contained in themicrocontroller 360 or memory 394) to be sent to the external device 302through an established communication link 304.

In certain implementations, the stimulation device 110 or 210 mayfurther include a physiologic sensor 308, commonly referred to as a“rate-responsive” sensor to adjust pacing stimulation rate according tothe exercise state of the patient. However, the physiological sensor 308may further be used to detect changes in cardiac output, changes in thephysiological condition of the heart, or diurnal changes in activity(e.g., detecting sleep and wake states). Accordingly, themicrocontroller 360 responds by adjusting the various pacing parameters(such as rate, stimulation delays, etc.) at which the atrial andventricular pulse generators 370, 372 generate stimulation pulses.

A common type of rate responsive sensor is an activity sensor, such asan accelerometer or a piezoelectric crystal, which is mounted within thehousing 340 of the stimulation device 110 or 210. Other types ofphysiologic sensors are also known, for example, sensors which sense theoxygen content of blood, respiration rate, and/or minute ventilation, pHof blood, ventricular gradient, etc. However, any suitable sensor may beused which is capable of sensing a physiological parameter whichcorresponds to the exercise state of the patient. The type of sensorused is not critical to the present disclosure and is shown only forcompleteness.

The stimulation device 110 or 210 additionally includes a battery 310which provides operating power to all of the circuits shown in FIG. 3 .For the stimulation device 110 or 210, which employs shocking therapy,the battery 310 must be capable of operating at low current drains forlong periods of time, and then be capable of providing high-currentpulses (for capacitor charging) when the patient requires a shock pulse.The battery 310 must also have a predictable discharge characteristic sothat elective replacement time can be detected. Accordingly, the device110 or 210 preferably employs lithium/silver vanadium oxide batteries,as is true for most (if not all) current devices.

The device 110 or 210 is shown in FIG. 3 as having an impedancemeasuring circuit 312 which is enabled by the microcontroller 360 via acontrol signal 314. The known uses for an impedance measuring circuit312 include, but are not limited to, lead impedance surveillance duringthe acute and chronic phases for detecting proper lead positioning ordislodgement; detecting operable electrodes and conductors; andautomatically switching to an operable pair if dislodgement orelectrical disruption occurs; measuring respiration or minuteventilation; measuring thoracic impedance for determining shockthresholds; detecting when the device has been implanted; measuringstroke volume; and detecting the opening of heart valves, etc. Theimpedance measuring circuit 312 is advantageously coupled to the switch374 so that any desired electrode may be used.

In certain implementations of the present disclosure, the device 110 or210 may be configured to perform beat-by-beat impedance monitoring inconjunction with measuring and monitoring other electrical activity(e.g., generating IEGMs) for each beat. In such applications, themeasured impedance may generally provide further information regardingthe occurrence and potential cause of changes in the electricalactivity, including, without limitation, changes in His bundle capturetype or capture quality.

According to one implementation of the present disclosure, the His tipelectrode 116 (or 216) and His ring electrode 119 (or 219) may beselectively coupled via switch 374 to the impedance measuring circuit312 for performing a tissue impedance measurement. The tissue impedancemeasurement may be made to determine the location of the His bundle asthe His tip electrode 116 (or 216) or mapping collar 418 as shown inFIG. 4 , or sensing electrodes advanced along the endocardial surface ofthe right atrium. In other implementations of the present disclosure,alternative approaches for mapping the intrinsic conduction signals ofthe His bundle and associated tissue may be used. For example andwithout limitation, in at least one implementation an electrophysiology(EP) catheter may be used to identify a location for the His tipelectrode 116 (or 216).

In the case where the stimulation device 110 or 210 is intended tooperate as an implantable cardioverter/defibrillator (ICD) device, itmust detect the occurrence of an arrhythmia, and automatically apply anappropriate electrical shock therapy to the heart aimed at terminatingthe detected arrhythmia. To this end, the microcontroller 360 furthercontrols a shocking circuit 316 by way of a control signal 318. Theshocking circuit 316 generates shocking pulses of low (for example, upto 0.5 joules), moderate (for example, 0.5-10 joules), or high energy(for example, 11-40 joules), as controlled by the microcontroller 60.Such shocking pulses are applied to the patient's heart 112 through atleast two shocking electrodes, and as shown in this embodiment, selectedfrom the left atrial coil electrode 128, the right ventricular coilelectrode 136 (or 236), and the SVC coil electrode 138. As noted above,the housing 340 may act as an active electrode in combination with theright ventricular electrode 136, or as part of a split electrical vectorusing the SVC coil electrode 138 or the left atrial coil electrode 128(i.e., using the right ventricular electrode 136 as a common electrode).As previously noted, the implementation illustrated in FIG. 1 isprovided as an example and other configurations are possible. Forexample, in other implementations, the high voltage coils for both RVcoil and SVC coil may be disposed on the right ventricle lead as opposedto the RA lead.

Cardioversion shocks are generally considered to be of low to moderateenergy level (so as to minimize pain felt by the patient), and/orsynchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5-40joules), delivered asynchronously (since R-waves may be toodisorganized), and pertaining exclusively to the treatment offibrillation. Accordingly, the microcontroller 60 is capable ofcontrolling the synchronous or asynchronous delivery of the shockingpulses.

A more detailed illustration of the His bundle lead 121 (or 221) isshown in FIG. 4 . At the distal end of the lead 121 (or 221) is the Hisbundle tip electrode 116 (or 216). The His bundle tip electrode 116 (or216) is, or includes, an active fixation device, such as a helical,“screw-in,” device that allows stable fixation of the electrode in theHis bundle tissue.

The distal end of the His bundle lead 121 (or 221) is further providedwith a non-traumatic conductive surface (also referred to hereininterchangeably as a mapping collar) 418. The non-traumatic conductivesurface 418 is advantageously used to make electrical measurements thatindicate the location of the His bundle without having to anchor the Hisbundle tip electrode 116 (or 216) into the endocardial tissue. Thenon-traumatic conductive surface 418 and the His bundle tip electrode116 are electrically coupled within the lead body of the His bundle lead121 (or 221) and together form one conductive element for the purposesof sensing, stimulation, and impedance measurements.

The His bundle lead 121 (or 221) is also provided with a His ringelectrode 119 (or 216). The His ring electrode 119 (or 219) ispreferably spaced between approximately 2 mm and 30 mm, but preferably10 mm, from the His tip electrode 116 (or 216). The His ring electrode119 (or 219) may function as the return electrode during bipolarsensing, stimulation or impedance measurement operations.

The His tip electrode 116 (or 216) and the His ring electrode 119 (or219) are each connected to flexible conductors 464, 466, respectively,which may run the entire length of the His bundle lead 121 (or 221). Theflexible conductor 464 is connected to the His tip electrode 116 (or216) and is electrically insulated from the flexible conductor 466 by alayer of insulation. The conductor 466 is connected to the His ringelectrode 119 (or 219). The flexible conductors 464, 466 serve toelectrically couple the His ring electrode 119 (or 219) and the His tipelectrode 116 (or 216) to the His ring electrode terminal 351 and theHis tip electrode terminal 350, respectively. One embodiment of the Hisbundle lead 121 (or 221) is available from St. Jude Medical CRMD as leadmodel No. 2088T.

In accordance with certain embodiments, an excitation current is appliedthrough the His tip electrode 116 (or 216). A voltage signal can then bemeasured between the His tip electrode 116 (or 216) (or thenon-traumatic conductive surface 418) and the His ring electrode 119 (or219) in a bipolar fashion. The voltage signal is related to the suppliedcurrent and the tissue impedance associated with the tissue in contactwith the His tip electrode 116 (or 216). Thus, the measured voltagesignal is processed by the impedance measuring circuit 312 to determinethe impedance of the tissue in contact with His tip electrode 116 (or216). The impedance equals the voltage divided by the current.

The His tip electrode 116 (or 216) may then be secured in the His bundlethereby anchoring the His tip electrode 116 (or 216) in contact with theHis bundle tissue. The electrogram signal arising from the His bundlecan then be received by the His sensing circuit 383. A bypass filter(not shown) that allows signals ranging from 30-200 Hz to be receivedmay be used to block the high frequency alternating current excitationsignal produced by an oscillator.

It should be appreciated that the His bundle lead and associatedcomponents illustrated in FIG. 4 are provided merely as examples andshould not be viewed as limiting this disclosure to requiring anyparticular type of lead. Rather, aspects of the present currentdisclosure may be implemented using any suitable His bundle lead capableof being implanted at or near the His bundle and providing pacingimpulses to the His bundle. Further, it should be noted that instead ofusing a His bundle lead to deliver HBP pulses, and to sense His IEGMs,it would also be possible to use a leadless cardiac pacemaker (LCP) thatis implanted at least partially within or adjacent to the His bundle todeliver HBP pulse, and/or sense His IEGMs.

Referring again to FIG. 3 , the microcontroller 360 is also shown asincluding an atrial oversense detector 366, an atrial capture detector367, and an AV node capture detector 368. The atrial oversense detector366 is configured to perform an atrial oversensing test to determine,inter alia, whether or not atrial oversensing is detected within a HisIEGM. Additional details of various such atrial oversensing tests,according to embodiments of the present technology, are described belowwith reference to FIGS. 5-9 . The atrial capture detector 367 isconfigured to perform an atrial capture test to determine whether atrialcapture occurs in response to his bundle pacing (HBP). Additionaldetails of such an atrial capture test are described below withreference to FIGS. 10-11 . The AV node capture detector 368 isconfigured to perform an AV node capture test to determine whether AVnode capture occurs in response to HBP. Additional details of such an AVnode capture test are described below with reference to FIGS. 11-12 .More generally, the detectors 366, 367, and 368, which can also bereferred to as modules, can be used to implement various algorithmsand/or methods presented below in the discussion of FIGS. 5-13 . Theaforementioned detectors 366, 367, and 368 may be implemented inhardware as part of the microcontroller 360, or as software/firmwareinstructions programmed into the device 110 or 112 and executed on themicrocontroller 360 during certain modes of operation. More generally,the detectors 366, 367, and 368 can be implemented using one or moreprocessors.

Atrial Oversensing Testing

As noted above, the close proximity of the His bundle to thebasal-septal atrial myocardium, AV node, and basal-septal ventricularmyocardium presents unique challenges to medical personnel that performimplants, especially those new to His implants. For example, a largeatrial signal component, if present on a His bipolar or unipolar IEGM,can cause atrial oversensing and have undesirable consequences. Forexample, where a device algorithm for automated measurement of Hiscapture type and threshold relies on a bipolar and unipolar evokedresponse, such an algorithm may provide inaccurate results if atrialoversensing occurs. Certain embodiments of the present disclosure, whichare related to atrial oversensing testing, can be used to determinewhether or not atrial oversensing is occurring, and the results of suchtesting can be used to determine when it is appropriate to perform Hisbundle capture threshold detection and/or other types of His capturemanagement. Exemplary techniques for performing His bundle capturethreshold detection and/or other types of His capture management aredescribed in commonly assigned U.S. Provisional Patent Application No.62/948,047, titled AUTOMATIC PACING IMPULSE CALIBRATION USING PACINGRESPONSE TRANSITIONS filed Dec. 13, 2019, which was incorporated hereinby reference above. Since certain HBP capture management techniques relyon robust pacing of the His bundle and accurate sensing of theventricular evoked response, it is beneficial to only utilizes such HBPcapture management techniques in the absence of atrial oversensing (aswell as in the absence of atrial capture and AV node capture).

Various embodiments of the present technology, which relate to atrialoversensing testing, are described below with reference to FIGS. 5-9 .In accordance with certain embodiment, the atrial oversensing testingdescribed with reference to FIGS. 5-9 can be performed by or under thecontrol of the atrial oversense detector 366, or more generally, using acontroller that includes one or more processors and/or a state machine.

FIG. 5 is a high level flow diagram that is used to describe certainmethods for determining whether or not atrial oversensing is detectedwithin a His IEGM. Such methods can be used with an implantable medicaldevice (e.g., 102 or 202) including one or more electrodes that can beused for sensing and pacing, wherein such a device can make up an entireimplantable medical system, or may just be part of (e.g., a subsystemof) an implantable medical system.

Referring to FIG. 5 , step 502 involves obtaining an intracardiacelectrogram (IEGM) sensed using at least one electrode implanted in orproximate to a patient's His bundle. Since the IEGM obtained at step 502is sensed using at least one electrode implanted in or proximate to apatient's His bundle, such an IEGM can be referred to more specificallyas a His IEGM. The His IEGM obtained at step 502 can be a unipolar HisIEGM, wherein a case electrode (e.g., 340) is used as one of the sensingelectrodes to obtain the unipolar His IEGM. Alternatively, oradditionally, the His IEGM obtained at step 502 can be a bipolar HisIEGM, wherein at least two electrodes, not including the case electrode(e.g., 340), are used as the sensing electrodes to obtain the bipolarHis IEGM. For specific examples, referring back to FIGS. 1-3 , the Histip electrode 116 or 216 (connected His tip electrode terminal 350) andthe case electrode 340 can be used to sense a unipolar His IEGM; or theHis tip electrode 116 or 216 (connected to the His tip electrodeterminal 350) and the His ring electrode 119 or 219 (connected to theHis ring electrode terminal 351) can be used to sense a bipolar HisIEGM. FIG. 6 , discussed below, shows examples of His unipolar andbipolar IEGMs that could be obtained at step 502.

Referring again to FIG. 5 , step 504 involves sensing or pacing apatient's right atrium to thereby sense or pace an atrial event. A pacedatrial event can also be referred to as an atrial pace (AP), and asensed intrinsic atrial event can also be referred to as an atrial sense(AS). Step 504 can be performed, e.g., using at least one of theelectrodes of the right atrial lead 120, but is not limited thereto.

Step 506 involves determining whether a portion of the His IEGM exceedsa specified sense threshold within a specified window that begins anatrioventricular delay (AVD) following the sensed or paced atrial event.Such a step can be performed by comparing samples of the His IEGM to thespecified sense threshold, to thereby determine whether or not at leastone of the samples exceeds the specified sense threshold.

Step 508 is a decision block or step, which directs flow to step 510 orto step 524, depending upon the results of step 506. More specifically,at step 508 there is a determination of whether or not there was adetermination (at step 506) that a portion of the His IEGM exceeded thespecified sense threshold within the specified window. If the answer tothe determination at step 508 is No, then flow goes to step 524 and itis concluded that no atrial oversensing was detected. However, if theanswer to the determination at step 508 is Yes, then flow goes to step510. While steps 506 and 508 are shown as two distinct steps in FIG. 5 ,these steps can alternatively be combined into a single step, as wouldbe appreciated by one skilled in the art.

In accordance with certain embodiments, the specified window, whichbegins at the AVD following the sensed or paced atrial event (i.e.,following the AS or AP) is an evoked response window. In suchembodiments, step 506 can involve triggering the evoked response window(at the AVD following the sensed or paced atrial event) by delivering asubthreshold pacing pulse to the patient's His bundle (using at leastone electrode that is implanted in or proximate to the patient's Hisbundle), wherein the subthreshold pacing pulse has energy below acapture threshold associated with the patient's His bundle and the RVmyocardium. The subthreshold pacing pulse can, e.g., have an amplitudeof 0.25V and a pulse width of 0.05 ms, or can have the minimum amplitudeand minimum pulse width setting allowed by the implantable device, butis not limited thereto. Indeed, the subthreshold pacing pulse can havean amplitude of 0V if desired/possible, since its goal is not to causecapture, but rather, is to trigger an evoked response window. For theembodiments summarized with reference to the flow diagram of FIG. 5 ,the AVD (at the end of which the specified window, e.g., the evokedresponse window, begins) is preferably short enough such that intrinsicAV conduction does not occur within the specified window (e.g., theevoked response window) within which there is a determination of whetherthe specified threshold is crossed. For an example, assuming the deviceperforming the method of FIG. 5 is in DDD mode, the AVD used at step 506can be set to 50 ms following an atrial paced event (aka AP), or the AVDused at step 506 can be set to 25 ms following an atrial sensed event(aka AS). The use of longer or shorter AVD values are also possible, andwithin the scope of the embodiments described herein. In accordance withcertain embodiments, the length of the specified window (e.g., theevoked response window) within which there is a determination of whetherthe specified threshold is crossed can be 140 ms, or more generallywithin the range of 120 ms to 160 ms. The use of windows that are longeror shorter than that range are also possible, and within the scope ofthe embodiments described herein. In accordance with certainembodiments, at the end of the specified window a safety pacing pulse(aka a backup pacing pulse) is delivered to the right ventricle.

In summary, steps 502-508 are performed to determine whether or notatrial oversensing may have potentially occurred. If the answer to thedetermination at step 508 was No, then as noted above, it is concludedat step 524 that atrial oversensing was not detected. If the answer tothe termination at step 508 was Yes, then as noted above, flow goes tostep 510. As will be appreciated from the below discussion, steps510-520 are performed to determine whether or not the His IEGM exceedingthe specified sense threshold within the specified window (whichresulted in the answer to the determination at step 508 being Yes) wasdue to atrial oversensing, as opposed to some other factor such asnoise, a pacing artifact (if subthreshold pacing has an amplitudegreater than 0V), or a premature ventricular contraction (PVC).

Still referring to FIG. 5 , step 510 involves determining a first onsetinterval corresponding to a length of time between a beginning of thespecified window and when the portion of the His IEGM exceeded thespecified sense threshold within the specified window. Step 512 involvessensing or pacing the right atrium of the patient to thereby sense orpace a further atrial event. Step 514 involves determining whether aportion of the IEGM exceeds the specified sense threshold within afurther specified window that begins at an extended AVD following thefurther sensed or paced atrial event, wherein the extended AVD is equalto the specified AVD (referred to in step 506) plus an extensioninterval that is less than the first onset interval. For an example, theextension interval can be a fixed value, such as 50 ms. Alternatively,the extension interval can be dynamically determined based on the firstonset interval that we determined at step 510. More specifically, theextension interval can be equal to a specified percentage (e.g., 50%) ofthe first onset interval, but is not limited thereto. Assuming that theextension interval is equal to 50% of the first interval, then theextended AVD would be equal to the specified AVD (referred to in step506) plus 50% of the first onset interval (determined at step 510). Inaccordance with certain embodiments, the further specified window(referred to in step 514) can be a further evoked response window thatis triggered by delivering a further subthreshold pacing pulse havingenergy below a capture threshold associated with the patient's Hisbundle and the RV myocardium. Step 516 is a decision block or step,which directs flow to step 518 or to step 524, depending upon theresults of step 514. More specifically, at step 516 there is adetermination of whether or not a portion of the IEGM exceeds thespecified sense threshold within the further specified window thatbegins at the extended AVD following the further sensed or paced atrialevent. If the answer to the determination at step 516 is No, then flowgoes to step 524 and it is concluded that no atrial oversensing wasdetected. However, if the answer to the determination at step 516 isYes, then flow goes to step 518. While steps 514 and 516 are shown astwo distinct steps in FIG. 5 , these steps can alternatively be combinedinto a single step, as would be appreciated by one skilled in the art.In accordance with certain embodiments, at the end of the furtherspecified window a safety pacing pulse (aka a backup pacing pulse) isdelivered to the right ventricle.

Step 518 involves determining a second onset interval corresponding to alength of time between a beginning of the further specified window andwhen the portion of the IEGM within the further specified window exceedsthe specified sense threshold.

Step 520 involves determining whether the second onset interval is equalto the first onset interval minus the extension interval. Step 520 is adecision block or step, which directs flow to step 522 or to step 524,depending upon the results of steps 518 and 510. More specifically, atstep 520 there is a determination of whether or not the second onsetinterval (determined at step 518) is equal to the first onset interval(determined at step 510) minus the extension interval (referred to instep 514). If the answer to the determination at step 520 is No, thenflow goes to step 524 and it is concluded that no atrial oversensing wasdetected. However, if the answer to the determination at step 520 isYes, then flow goes to step 522, and it is concluded that atrialoversensing was indeed detected.

Example His bipolar and His unipolar IEGMs, one or both of which can bedetected at an instance of step 502, are shown in FIG. 6 and will now beused to explain in more detail how atrial oversensing may be detectedusing the embodiment summarized with reference to the flow diagram ofFIG. 5 . Referring to FIG. 6 , the time t1 corresponds to a time atwhich an atrial sensed event (AS) occurred, which AS could be detectedat step 504. Still referring to FIG. 6 , the time t2 corresponds to a 25ms AVD following the AS that occurred at the time t1, at which point intime the specified window referred to in step 506 begins. In otherwords, the 25 ms AVD is an example of the AVD referred to in step 506.The horizontal dotted lines in FIG. 6 are representative of thespecified sense threshold (referred to in steps 506 and 508), for whichthere is a determination of whether the specified threshold is crossedby the His IEGM.

In FIG. 6 , the “search window” 602 corresponds to the specified windowreferred to in step 506, and more specifically, corresponds to thespecified window (that begins the AVD following the sensed or pacedatrial event) within which there is a determination of whether a portionof the His IEGM exceeds a specified sense threshold. In certainembodiments, the specified window 602 (which can also be referred to asthe search window) is an evoke response window that is triggered bydelivering a subthreshold pacing pulse, as was discussed above withreference to step 506 in FIG. 5 .

In FIG. 6 , the time t3 corresponds to a time at which a portion of theHis IEGM exceeds the specified sense threshold within the specifiedwindow. The interval between the time t2 and the time t3 corresponds tothe first onset interval, which is determined at step 510 in FIG. 5 .The time t4 is the end of the search window, and thus the search window(aka the specified window) corresponds to the interval between the timet2 and the time t4, in this example.

Still referring to FIG. 6 , the time t5 corresponds to a time at which afurther atrial sensed event (AS) occurred, which AS could be detected atstep 512. The time t6 corresponds to an extended AVD following the ASthat occurred at time t5, at which point in time the further specifiedwindow 612 referred to in step 514 begins. In other words, the 55 ms AVDis an example of the extended AVD referred to in step 514, wherein theextended AVD in this example is equal to the 25 ms AVD (referred to instep 506) plus 50% of the 60 ms first onset interval determined at step510, and thus in this example the extended AVD is equal to 55 ms (i.e.,25 ms+0.50*60 ms=55 ms).

In FIG. 6 , the time t7 corresponds to a time at which a portion of theHis IEGM exceeds the specified sense threshold within the furtherspecified window 612. The interval between the time t6 and the time t7corresponds to the second onset interval, which is determined at step518 in FIG. 5 . The time t8 is the end of the search window 612, andthus the search window (aka the further specified window) corresponds tothe interval between the time t6 and the time t8, in this example. Inthe example of FIG. 6 , the 30 ms second onset interval is indeed equalto the 60 ms first onset interval minus the 30 ms extension interval,and this, the answer to the determination at step 520 in FIG. 5 would beYes, thereby resulting in atrial oversensing being detected at step 522in FIG. 5 . Due to the intrinsic delay of the AV node, any ventricularsignal would occur outside of the search window, as demonstrated in FIG.6 . Only an atrial signal could occur in the search window and result inidentical t1 to t3 and t5 to t7 intervals.

In FIG. 6 , both a His bipolar IEGM was shown (at the top of the page),and a His unipolar IEGM was shown (at the bottom of the page). However,both types of His IEGMs need not be sensed or used to perform an atrialoversensing test described above with reference to FIG. 5 .Nevertheless, if both types of His IEGMs are available for analysis,since both are sensed, the method can be performed for each of the typesof His IEGMs, and depending upon the specific implementation, atrialoversensing can be detected when step 522 is reached for at least one ofthe His IEGMs, or for both of the His IEGMs. The method of FIG. 5 canalternatively be performed for just one of the types of His IEGMs (i.e.,unipolar or bipolar).

The medical system, with which an embodiment summarized with referenceto FIGS. 5 and 6 is performed, can be configured to selectively performHis capture management. In such a medical system, whenever atrialoversensing is detected, His capture management is not performed,because the His capture management would likely be adversely affected bythe atrial oversensing. In other words, in accordance with certainembodiments, a method can include preventing performance of the Hiscapture management in response to detecting atrial oversensing. In suchan embodiments, after detecting atrial oversensing, at a later point intime that atrial oversensing is no longer detected, performance of theHis capture management is enabled. The aforementioned His capturemanagement can include determining whether His capture occurred inresponse to delivery of a pacing pulse, determining a capture threshold(e.g., performing His Autocapture), and/or determining a capture typewhen capture is determined to have occurred.

The embodiments described with reference to FIGS. 5 and 6 are especiallyuseful when an implantable stimulation system/device is in DDD mode,since such a system/device performs pacing at the His lead a specifiedAVD following an AS or AP if a PVC is not encountered during thespecified AVD. Since DDD mode does not provide for a backup pacing pulseat the end of each specified window, delivery of a backup pacing at theend of the search window is preferably programmed into the atrialoversensing test. In accordance with certain embodiments, an implantablestimulation system/device is programmed to deliver a backup pulse to theHis bundle at the end of each specified window, which in certainembodiments, are evoked response windows. Each such window (e.g., evokedresponse window) preferably ends before intrinsic AV conduction isexpected. This can be achieved by using sufficiently short AVDs whenmonitoring for atrial oversensing, and sufficiently short windows (e.g.,evoked response windows).

FIGS. 7A and 7B, which can be collectively referred to as FIG. 7 ,include a high level flow diagram that is used to describe methods fordetermining whether or not atrial oversensing may occur, and if so, howto characterize the atrial oversensing and/or reduce the likelihood offurther atrial oversensing. Such methods can be used with an implantablemedical device (e.g., 102 or 202) including one or more electrodes thatcan be used for sensing and pacing, wherein such a device can make up anentire implantable medical system, or may just be part of (e.g., asubsystem of) an implantable medical system.

Referring to FIG. 7A, step 702 involves obtaining an IEGM sensed usingat least one electrode implanted in or proximate to a patient's Hisbundle. Since the IEGM obtained at step 702 is sensed using at least oneelectrode implanted in or proximate to a patient's His bundle, such anIEGM can be referred to more specifically as a His IEGM. Step 702 is thesame as step 502 described above with reference to FIG. 5 , and thus,additional details of step 702 can be appreciated from the abovediscussion of step 502.

Still referring to FIG. 7A, step 704 involves sensing or pacing apatient's right atrium to thereby sense or pace an atrial event. A pacedatrial event can also be referred to as an atrial pace (AP), and asensed intrinsic atrial event can also be referred to as an atrial sense(AS), as was noted above in the discussion of step 504. Step 704 can beperformed, e.g., using at least one of the electrodes of the rightatrial lead 120, but is not limited thereto.

Step 706 involves determining whether a portion of the His IEGM exceedsa specified sense threshold within a specified window that is within anAVD following the sensed or paced atrial event. More specifically, thespecified window coincides with a portion of the AVD, but is preferablyshorter than the AVD. Step 706 can be performed by comparing samples ofthe His IEGM to the specified sense threshold, to thereby determinewhether or not at least one of the samples exceeds the specified sensethreshold. In contrast to the AVD referred to in step 506 above, the AVDused at step 706 is preferably an extended AVD that is long enough toallow for intrinsic atrioventricular (AV) conduction within the AVD, inwhich case this test can be performed while the system/device is in DDDmode. When intrinsic AV conduction is not detected, i.e., no thresholdcrossing is detected outside of the specified window, a backup pacingpulse should preferably be delivered at the end of the AVD. For anexample, the AVD used at step 706 can be set to 350 ms following anatrial paced event (aka AP), or the AVD used at step 706 can be set to300 ms following an atrial sensed event (aka AS), as noted above. Wherethe AVD used at step 706 is 350 ms following an AP, then the specifiedwindow (within which it is determined whether the His IEGM exceeds thespecified sense threshold) can, e.g., correspond to the first 160 ms ofthe 350 ms AVD. Where the AVD used at step 706 is 300 ms following anAS, then the specified window (within which it is determined whether theHis IEGM exceeds the specified sense threshold) can, e.g., correspond tothe first 100 ms of the 300 ms AVD. The use of longer or shorter AVDvalues and window lengths are also possible, and within the scope of theembodiments described herein. If the AVD referred to in step 706 is notlong enough to allow for intrinsic AV conduction within the AVD, thenthe test should be performed while the system/device is in DDT mode, inwhich case ventricular pacing can be triggered at an end of the AVD.Additionally or alternatively, ventricular pacing can be triggered inresponse to atrial oversensing being detected, or more specifically, inresponse to detecting a portion of the His IEGM exceeding the specifiedsense threshold within the AVD.

Step 708 is a decision block or step, which directs flow to step 710 orto step 724, depending upon the results of step 706. More specifically,at step 708 there is a determination of whether or not there was adetermination (at step 706) that a portion of the His IEGM exceeded thespecified sense threshold within the specified window. If the answer tothe determination at step 708 is No, then flow goes to step 712 and itis concluded that no atrial signal component was detected, and thus,that atrial oversensing is not a concern. However, if the answer to thedetermination at step 708 is Yes, then flow goes to step 710 and it isconcluded that an atrial signal component was detected and that atrialoversensing is possible, and thus, is a potential concern. Followingstep 710, flow goes to step 714 in FIG. 7B. The steps show in FIG. 7Bcan be used to characterize potential atrial oversensing and/or reducethe likelihood of further atrial oversensing.

While steps 706 and 708 are shown as two distinct steps in FIG. 7A,these steps can alternatively be combined into a single step, as wouldbe appreciated by one skilled in the art. Flow can go directly from step710 to step 714, as shown in FIGS. 7A and 7B. Alternatively, in responseto detecting an atrial signal component (which may cause oversensing),steps 702-708 can be repeated one or more time(s) to confirm thedetection of an atrial signal component within the His IEGM, before flowgoes to step 714. In other words, step 714 can be performed in responseto detecting an atrial signal component within the His IEGM, orconfirmation thereof. Step 714-726 can be performed for or using a sameone or more cardiac cycle analyzed at steps 702-710, or for or using oneor more cardiac cycles thereafter.

Step 714 involves determining an atrial event-to-threshold crossinginterval corresponding to a length of time between a paced or sensedatrial event and a respective crossing of the specified sense thresholdwithin the specified window (that is within the AVD).

Step 716 then involves specifying an atrial oversensing avoidance (AOA)period based on the atrial event-to-threshold crossing interval, whereinthe AOA period corresponds to when atrial oversensing may occurfollowing paced or sensed atrial events. Flow then goes to step 718.

Step 718 involves detecting a peak amplitude of the portion of the IEGMthat exceeds the specified sense threshold within the AOA period. Step720 involves detecting a peak of a portion of the IEGM, following theAOA period, that corresponds to a ventricular depolarization. Step 722involves determining a ratio of the peak amplitude within the AOA periodto the peak amplitude following the AOA period (that corresponds to aventricular depolarization). Since the ratio determine at step 722 is aratio of the amplitudes of an atrial signal component relative to aventricular signal component, the ratio can also be referred to morespecifically as the A/V ratio. In accordance with certain embodiments,the AOA period can be a period of fixed length that is temporallycentered about where the atrial signal component was detected inresponse to the threshold crossing. It is also possible that the AOAperiod is rate dependent, such that it is inversely proportional to apatient's heart rate, or is proportion to a patient's VV interval, orthe like. It is also possible that the AOA period is not is temporallycentered about where the atrial signal component was detected. Othervariations are also possible, and within the scope of the embodimentsdescribed herein.

At step 724 there is a determination of whether or not the A/V ratio(determined at step 722) exceeds a ratio threshold. Step 726 is adecision block or step, which directs flow to step 728 or to step 730,depending upon the results of step 726. More specifically, at step 726there is a determination of whether or not there was a determination (atstep 724) that the A/V ratio (determined at step 722) exceeds the ratiothreshold. If the answer to the determination at step 726 is No, thenflow goes to step 730 and it is concluded that there is no need to usean atrial oversensing avoidance technique, since the atrial signalcomponent is relatively small compared to the ventricular signalcomponent, and thus, it is unlikely that an atrial signal component willbe mistakenly detected as a ventricular signal component. However, ifthe answer to the determination at step 728 is Yes, then flow goes tostep 728 and it is concluded that an atrial oversensing avoidancetechnique should be used. In other words, if flow goes to step 728 thenatrial oversensing is considered to be a concern. While steps 724 and726 are shown as two distinct steps in FIG. 7B, these steps canalternatively be combined into a single step, as would be appreciated byone skilled in the art. The same sense threshold that is used within theAOA period (to detect a portion of the IEGM exceeding the sensethreshold) can be used to detect a ventricular depolarization followingAOA period, or a different threshold can be used, depending uponimplementation.

If it is determined at step 728 that atrial oversensing is a potentialconcern, an alert can be issued to the patient and/or a medicalpersonnel. Additionally, or alternatively, detected atrial signalcomponents can be recorded in a log. If atrial signal components are notdetected for at least some length of time, then there may be no need tocontinue to search for a portion of the IEGM within the AOA periodexceeding the specified sense threshold. In other words, a so called AOAtechnique can be disabled if no atrial signal components are detected,or more generally it atrial oversensing is not determined to be apotential concern.

After specifying the AOA period, and while the implantable medicalsystem is in DDD mode, further sensing or pacing of the right atrium ofthe patient occurs to thereby sense or pace an atrial event. In certainembodiments, in order to avoid further atrial oversensing, a multi-levelsense threshold is used to detect ventricular events following sensed orpaced atrial events, an example of which is shown in FIG. 8 . The use ofa multi-level sense threshold is one example of an atrial oversensingavoidance technique that may be used, in response to concluding thatatrial oversensing is a potential concern.

Referring to FIG. 8 , shown therein is an example His IEGM 802. Thedashed line 804 shown in FIG. 8 corresponds to a multi-level sensethreshold which can be used to avoid atrial oversensing between the timeof an AS or AP and a following ventricular depolarization represented bythe ventricular signal component in the His IEGM. As can be appreciatedfrom FIG. 8 , the multi-level sense threshold 804 is greater during anAOA period 806 than following the AOA period 806, in order to avoiddetecting the atrial signal component 808 during the AOA period 806.

The embodiments summarized with reference to FIGS. 7 and 8 can be usedto detect potential atrial oversensing and characterize amplitudes ofthe atrial and ventricular signal components of a His IEGM. In certainuses of such embodiments, wherein a system/device is in DDD mode withsensed/paced AVD of 300/350 ms (or some other values), the test appliesa low sensitivity (high sensing threshold) for a period to purposelyavoid sensing the atrial signal component 808 following AS/AP, thenreverts to high sensitivity to sense the ventricular signal component810, as can be appreciated from FIG. 8 . The period of low sensitivityis the AOA period 806. The peak amplitude of atrial signal component808, if present, in the AOA period 806 is compared to the peak amplitudeof the ventricular signal component 810. Atrial oversensing can bedeclared if the A/V ratio is greater than a programmed threshold (e.g.0.5). The measured atrial and ventricular signal component peakamplitudes can also be used to program a dynamic AOA algorithm, whichcan use a multi-level sense threshold 804 such as the one shown in FIG.8 .

FIG. 9A includes a table (Table 1) that summarizes stim-to-onsetintervals of patient's with and without atrial oversensing, which tablecan be used to specify the length of the specified window used with theatrial oversensing test summarized with reference to FIGS. 5 and 6 .More specifically, based on the analysis of the clinical data shown inFIG. 9A, it was determined that 140 ms is an appropriate length of thespecified windows referred to in steps 506, 508, 514, and 516, althoughthe use of shorter and longer windows is also within the scope of theembodiments described herein.

FIG. 9B includes a table (Table 2) that summarizes AS/AP to onsetintervals of patient's with and without oversensing, which table can beused to specify the length of the specified window used with the atrialoversensing test summarized with reference to FIG. 7 . Morespecifically, based on the analysis of the clinical data shown in FIG.9B, it was determined that 100 ms is an appropriate length of thespecified windows referred to in steps 706 and 708, although the use ofshorter and longer windows is also within the scope of the embodimentsdescribed herein.

The embodiments of the present technology described above with referenceto FIG. 7 can be used to detect and further characterize atrialoversensing. When implementing such an embodiment, the specified sensethreshold that is used (at steps 706 and 708) is preferably relativelylow, to provide for high sensitivity. In a specific implementation, themedical device/system that implements such an embodiment is programmedto be in DDT mode, e.g., with a sensed/paced AVD of 150/200 ms. DDT modeensures ventricular pacing in case of atrial oversensing on the Hislead. If sensing occurs on the ventricular channel (VS), the intervalfrom the A sense/pace marker (AS/AP) to signal onset on the His lead ismeasured. At an example base rate of 60 bpm, the AS/AP to trueventricular sensing should be at least 120 ms and can be much longer inpatients with AV block or bundle branch block. Based on analysis ofclinical data (summarized in Table 2 of FIG. 9B), an AS/AP to VSinterval of less than 100 ms is a reliable indicator of atrialoversensing on the His IEGM. In certain embodiments, the peak amplitudefollowing VS can be measured in the sense refractory period. Both theAS/AP-VS interval and the peak amplitude of the VS can be measured formultiple consecutive beats. If the AS/AP to VS intervals areconsistently less than 100 ms (or some other specified temporalthreshold), atrial oversensing is confirmed. The AS/AP to VS intervalsthat are less than 100 ms (or some other specified temporal threshold)can be used to characterize when atrial oversensing could occur. Thepeak amplitudes of VS events that are within 100 ms (or some otherspecified temporal threshold) of the AS/AP event can be used to thecharacterize the amplitude of atrial oversensing. Other variations arealso possible, and within the scope of the embodiments described herein.

Atrial Capture Test

Where one or more electrodes (of a His lead or LCP) are implanted withinor proximate the His bundle, it is possible that undesirable directatrial capture may occur in response to HBP pulses being delivered tothe His bundle. Certain embodiments of the present technology describedbelow (with reference to FIGS. 10A, 10B, and 11A-11G) relate todetermining whether or not such atrial capture occurs. In accordancewith certain embodiment, the atrial capture test described withreference to FIGS. 10A, 10B, and 11A-11G can be performed by or underthe control of the atrial capture detector 367, or more generally, usingone or more processors.

FIGS. 10A and 10B, which can be referred to collectively as FIG. 10 ,include a high level flow diagram that is used to describe methods forperforming an atrial capture test, in accordance with certainembodiments of the present technology. Such a test can be used to detectif and/or when atrial capture occurs in response to pacing a patient'sHis bundle using at least one electrode that is implanted in orproximate to the patient's His bundle. Preferably, prior to performingthe atrial capture test described with reference to FIG. 10 , apatient's type of His bundle capture is determined using a His bundlecapture threshold test, such as, but not limited to, one described inU.S. Provisional Patent Application No. 62/948,047, titled AUTOMATICPACING IMPULSE CALIBRATION USING PACING RESPONSE TRANSITIONS filed Dec.13, 2019, which was incorporated herein by reference above. The Hisbundle pacing (HBP) capture type exhibited by a patient is dictated bythe His bundle anatomy of the patient, His lead/electrode location, andpacing pulse amplitude. The various HBP capture types that may occurinclude selective His bundle capture (S-HBP), nonselective His bundlecapture (NS-HBP), and myocardium only capture (Myo-HBP). The myocardiumonly capture (Myo-HBP) type of His bundle pacing can also be representedusing the nomenclature M-HPB. A patient having an implantedlead/electrode used to perform HBP can experience one of the followingfive different responses to amplitudes of HBP pulses being graduallydecremented over time until loss of capture (LOC) of the His or RVmyocardium occurs: (1) S-HBP to LOC; (2) NS-HBP to LOC; (3) Myo-HBP toLOC; (4) NS-HBP to S-HBP to LOC; or (5) NS-HBP to Myo-HBP to LOC. Suchgradually decrementing over time of HBP pulses until LOC of the His orRV myocardium occurs can be performed as part of a His bundle capturethreshold test, which may or may not be automated, depending upon thespecific implementation. The above listed five different responses canalso be referred to as His capture to LOC types.

Referring to FIG. 10 , step 1002 involves obtaining an IEGM sensed usingat least one electrode implanted in or proximate to a patient's Hisbundle. Since the IEGM obtained at step 1002 is sensed using at leastone electrode implanted in or proximate to a patient's His bundle, suchan IEGM can be referred to more specifically as a His IEGM. Step 1002 isthe same as step 502 described above with reference to FIG. 5 , andthus, additional details of step 1002 can be appreciated from the abovediscussion of step 502. Still referring to FIG. 10 , step 1004 involves,during a plurality of cardiac cycles during which pacing of a patient'sHis bundle occurs, using at least one electrode implanted in orproximate to a patient's His bundle to deliver pacing pulses to thepatient's His bundle, wherein the amplitudes of the pacing pulses aregradually decremented over time until there is loss of capture of theHis bundle or RV myocardium. In other words, step 1004 involvesgradually decremented over time amplitudes of pacing pulses that aredelivered to the patient's His bundle until loss of His or RV myocardiumcapture occurs, such that the patient's His bundle is paced at aplurality of different pacing pulse amplitudes.

Step referring to FIG. 10 , step 1006 involves, for each pacing pulseamplitude, of the different pacing pulse amplitudes used during thepacing of the patient's His bundle, determining a respectivestimulation-to-atrial sense (stim-to-AS) interval corresponding to alength of time between when a His pacing pulse having the pacing pulseamplitude is delivered and when a respective atrial sensed event occurs.Step 1008 involves detecting how many increases to the stim-to-ASinterval occurred, if any, in response to the pacing pulse amplitudesbeing gradually decremented over time until the loss of His or RVmyocardium capture occurs. Since patients will likely have some naturalvariation to their stim-to-AS intervals, an increase to the stim-to-ASinterval will only be considered to have occurred (at step 1008) if theincrease is significant, e.g., by at least some specified meaningfulamount (e.g., 25 ms) or by at least some specified meaningful percentage(e.g., 25%), which can be predetermined or programmable. Step 1008 canalso involve determining, detecting, or monitoring corresponding pacingpulse amplitudes, for reasons explained below. The remaining steps whichare described in further detail below, are used to determine whetheratrial capture occurred, during the pacing of the patient's His bundle,based on results of the detecting how many increases to the stim-to-ASinterval occurred, if any.

At step 1010 there is a determination of whether zero detected increasesto the stim-to-AS interval occurred (i.e., whether no increases to thestim-to-AS interval were detected). If the answer to the determinationat step 1010 is Yes, then flow goes to step 1012, and it is concludedthat atrial capture occurred, and that the atrial capture threshold isbelow the capture threshold of the His bundle. In other words, steps1010 and 1012 involve determining that atrial capture occurred if therewere zero detected increases to the stim-to-AS interval in response tothe pacing pulse amplitudes being gradually decremented over time untilthe loss of His or RV myocardium capture occurs. If the answer to thedetermination at step 1010 is No, then flow goes to step 1014.

At step 1014 there is a determination of whether the specific patient(for which the atrial capture test is being performed) has the specificHis bundle capture to LOC type NS-HBP to Myo-HBP to LOC, which can alsobe referred to more succinctly as NS-Myo-LOC. Such a patient willexperience nonselective (NS) His bundle capture at relatively high HBPpulse amplitudes, myocardium only capture (Myo-HBP) at somewhat lowerHBP pulse amplitudes, and then eventual complete loss of capture (LOC)of the His bundle and RV at even lower HBP pulse amplitudes. This is aspecial case type of patient, for which the steps described in FIG. 10Bshould be performed (instead of the steps 1016-1024 in FIG. 10A). Forpatient's having one of the other four types of His bundle to LOCcapture types, including: S-HBP to LOC (which can also be referred tomore succinctly as S-LOC); NS-HBP to LOC (which can also be referred tomore succinctly as (NS-LOC); Myo-HBP to LOC (which can also be referredto more succinctly as Myo-LOC); and NS-HBP to S-HBP to LOC (which canalso be referred to more succinctly as NS-S-LOC), flow should godirectly from step 1014 to step 1016. For this discussion, initially itwill be assumed that the answer to step 1010 is No, and that flow goesto step 1016.

At step 1016 there is a determination of whether there was only onedetected increase to the stim-to-AS interval that occurred (in responseto the pacing pulse amplitudes being gradually decremented over timeuntil the loss of His or RV myocardium capture occurred). If the answerto the determination at step 1015 is Yes, then flow goes to step 1018,and it is concluded that no atrial capture occurred. In other words,steps 1016 and 1018 involve determining that no atrial capture occurredif there was only one detected increase to the stim-to-AS interval inresponse to the pacing pulse amplitudes being gradually decremented overtime until the loss of His or RV myocardium capture occurs. If theanswer to the determination at step 1016 is No, then flow goes to step1020.

At step 1020 there is a determination of whether there were exactly twodetected increase to the stim-to-AS interval that occurred (in responseto the pacing pulse amplitudes being gradually decremented over timeuntil the loss of His or RV myocardium capture occurred). If the answerto the determination at step 1020 is Yes, then flow goes to step 1022,and it is concluded that atrial capture occurred, and that the atrialcapture threshold is above the capture threshold of the His bundle. Inother words, steps 1020 and 1022 involve determining that atrial captureoccurred if there were exactly two detected increases to the stim-to-ASinterval in response to the pacing pulse amplitudes being graduallydecremented over time until the loss of His or RV myocardium captureoccurs. If the answer to step 1020 is No, which should only occur wherethere are three or more increases to the stim-to-AS interval (inresponse to the pacing pulse amplitudes being gradually decremented overtime until the loss of His or RV myocardium capture occurs), this willbe treated as an error (since that should not occur) and the results ofthe atrial capture test will be considered indeterminate, as detected atstep 1024.

Returning to step 1014, if the answer to step 1014 was Yes, meaning theHis capture to LOC type of the patient is NS-Myo-LOC, then flow goes tostep 1026 in FIG. 10B. At step 1026 in FIG. 10B there is a determinationof whether there was only one detected increase to the stim-to-ASinterval that occurred. If the answer to the determination at step 1026is Yes, then flow goes to step 1028, and it is concluded that atrialcapture occurred, and that the atrial capture threshold is at or belowthe pulse amplitude at where the one stim-to-AS interval occurred. Inother words, steps 1026 and 1028 involve determining that atrial captureoccurred (in a patient have an NS-Myo-LOC His capture to LOC type) ifthere was only one detected increase to the stim-to-AS interval inresponse to the pacing pulse amplitudes being gradually decremented overtime until the loss of His or RV myocardium capture occurs. If theanswer to the determination at step 1026 is No, then flow goes to step1030.

At step 1030 there is a determination of whether there were exactly twodetected increases to the stim-to-AS intervals that occurred (inresponse to the pacing pulse amplitudes being gradually decremented overtime until the loss of His or RV myocardium capture occurred). If theanswer to the determination at step 1030 is Yes, then flow goes to step1032. At step 1032 there is a determination of whether the two increasesto the stim-to-AS intervals coincided with the patient's NS capturethreshold and the patient's Myo capture threshold. If the answer to thedetermination at step 1032 is Yes, then it is concluded that no atrialcapture occurred, as shown at step 1034. Rather, it is concluded thatthe first increase to the stim-to-AS interval was caused by a transitionfrom NS-to-Myo capture, and the second increase to the stim-to-ASinterval was caused by the transition from Myo-to-LOC.

If the answer to the determination at step 1032 is No, then flow goes tostep 1036. At step 1036 it is concluded that atrial capture occurred,and that the atrial capture threshold is at or below where the increaseto the stim-to-AS interval did not coincide with the NS capturethreshold or the Myo capture threshold.

Returning to step 1030, if the answer to the determination at step 1030was No, then flow goes to step 1038. At step 1038 there is adetermination of whether exactly three increases to the stim-to-ASintervals occurred (in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurred). If the answer to the determination at step 1038 isYes, then flow goes to step 1040. At step 1040 it is concluded thatatrial capture occurred, and that the atrial capture threshold is at orbelow where the first increase to the stim-to-AS interval occurred.

If the answer to the determination at step 1038 is No, which should onlyoccur where there are four or more increases to the stim-to-AS interval(in response to the pacing pulse amplitudes being gradually decrementedover time until the loss of His or RV myocardium capture occurs), thiswill be treated as an error (since that should not occur) and theresults of the atrial capture test will be considered indeterminate, asindicated at step 1042

FIG. 11A, which includes an example of an atrial bipolar IEGM (ABipolar) and a corresponding example His bipolar IEGM (His Bipolar) fora patient having one of the other four His bundle capture to LOC types,besides the NS-Myo-LOC type. FIG. 11A shows that the amplitudes of Hisbundle pacing (HBP) pulses are gradually decremented from 5V, to 4V, to3V, to 2V, to 1V, and that loss of capture (LOC) of the His bundle or RVoccurred at 1V. FIG. 11A also shows that in response to the gradualdecrementing of the amplitudes of the HBP pulses, the stim-to-ASinterval increased twice, including from 100 ms to 200 ms, and then from200 ms to 300 ms. Because there were exactly two increases to thestim-AS interval (in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs), at steps 1020 and 1022 of FIG. 10A, it would bedetermined that atrial capture occurred and that the atrial capturethreshold is above the His bundle capture threshold.

FIG. 11B includes a further example of an atrial bipolar IEGM (ABipolar) and a corresponding example His bipolar IEGM (His Bipolar) fora patient having one of the other four His bundle capture to LOC types,besides the NS-Myo-LOC His capture type. FIG. 11B, which includes anexample atrial bipolar IEGM (A Bipolar) and a corresponding example Hisbipolar IEGM (His Bipolar), is used to show another example of how theatrial capture test described with reference to FIG. 10 can be used todetermine whether atrial capture was detected. FIG. 11B shows that theamplitudes of HBP pulses are gradually decremented from 5V, to 4V, to3V, to 2V, to 1V, and that LOC of the His bundle or RV occurred at 1V.FIG. 11B also shows that in response to the gradual decrementing of theamplitudes of the HBP pulses, the stim-to-AS interval never increased,but rather, remained at 100 ms. In other words, FIG. 11B shows zeroincreases to the stim-to-AS interval. Because there were zero increasesto the stim-AS interval (in response to the pacing pulse amplitudesbeing gradually decremented over time until the loss of His or RVmyocardium capture occurs), at steps 1010 and 1012 of FIG. 10A, it wouldbe determined that atrial capture occurred and that the atrial capturethreshold is below the His bundle capture threshold.

FIG. 11C-11G include examples of atrial bipolar IEGMs (A Bipolar) andcorresponding examples His bipolar IEGMs (His Bipolar) for patientsspecifically having the NS-Myo-LOC His capture to LOC type. Each ofthese FIGS. shows that there is a transition from NS-HBP to Myo-HBP at3V, and that LOC occurs at 1V.

In FIG. 11C there are zero increases to the stim-to-AS interval shown.Because there were zero increases to the stim-AS interval (in responseto the pacing pulse amplitudes being gradually decremented over timeuntil the loss of His or RV myocardium capture occurs), at steps 1010and 1012 of FIG. 10A, it would be determined that atrial captureoccurred, and that the atrial capture threshold is below the His bundlecapture threshold.

In FIG. 11D there is exactly one increase to the stim-to-AS intervalshown. Because there was exactly one increase to the stim-AS interval(in response to the pacing pulse amplitudes being gradually decrementedover time until the loss of His or RV myocardium capture occurs), andthe patient has the NS-Myo-LOC His capture to LOC type, at steps 1026and 1028 in FIG. 10B it would be determined that atrial captureoccurred, and that the atrial capture threshold is at are below wherethe increase to the stim-to-AS interval occurred (i.e., at 1V or below).

In FIG. 11E there are exactly two increases to the stim-to-AS intervalshown, from 100 ms to 200 ms, and from 200 ms to 300 ms. Since thestim-to-AS interval increase from 100 ms to 200 ms did not occur at oneof the NS or Myo capture thresholds, and the patient has the NS-Myo-LOCHis capture type, at steps 1030, 1032 and 1036 in FIG. 10B it would bedetermined that atrial capture occurred, and that the atrial capturethreshold is at are below where the increase to the stim-to-AS intervaloccurred that did no coincide with the NS or Myo threshold (i.e., at 3Vor within the range of 2V to 3V).

In FIG. 11F there are exactly three increases to the stim-to-AS intervalshown, from 100 ms to 150 ms, from 150 ms to 200 ms, and from 200 ms to300 ms. Because there were exactly three increases to the stim-ASinterval (in response to the pacing pulse amplitudes being graduallydecremented over time until the loss of His or RV myocardium captureoccurs), and the patient has the NS-Myo-LOC His capture to LOC type, atsteps 1038 and 1040 of FIG. 10B, it would be determined that atrialcapture occurred, and that the atrial capture threshold is at or belowwhere the first increase to the stim-to-AS interval occurred (i.e., at5V or within the range of 4V to 5V).

In FIG. 11G there are exactly two increases to the stim-to-AS intervalshown, from 150 ms to 200 ms, and from 200 ms to 300 ms. In FIG. 11G,the two increases to the stim-to-AS interval coincided with the NS andMyo capture thresholds, i.e., the increase from 150 ms to 200 mscoincided with the NS capture threshold, and the increase from 200 ms to300 ms coincided with the Myo capture threshold. Accordingly, it wouldbe determined at step 1030, 1032, and 1034 in FIG. 10B that atrialcapture did not occur.

Certain embodiments described with reference to FIGS. 10A, 10B and11A-11G take advantage of the fact that capture of the His bundle in NScapture results in a shorter retrograde conduction time compared to Myocapture. Such embodiments also take advantage of the fact that in theabsence of atrial capture, the Stim-AS interval measures the retrogradeconduction and should increase only when the loss of His capture occurs.Therefore, a sudden increase in the Stim-AS interval at the transitionfor NS capture to Myo capture should not trigger an atrial capturedetection.

AV Node Capture Test

Due to the close proximity of the His bundle to the AV node, it would bebeneficial to check if a His lead/electrode being implanted isundesirable in or contacting the AV node, before completing an implantprocedure. Because of the slow conduction through the AV node, AV nodepacing may result in long stim-onset interval (e.g., greater than 140ms) in the absence of atrial oversensing. An AV node capture test,according to certain embodiments of the present technology, is describedbelow with reference to the high level flow diagram of FIG. 12 , as wellas with reference to FIG. 13 . In accordance with certain embodiment,the AV node capture testing described with reference to FIGS. 12 and 13can be performed by or under the control of the AV node capture detector368, or more generally, using one or more processors.

Referring to FIG. 12 , step 1202 involves obtaining an intracardiacelectrogram (IEGM) sensed using at least one electrode implanted in orproximate to a patient's His bundle. Since the IEGM obtained at step1202 is sensed using at least one electrode implanted in or proximate toa patient's His bundle, such an IEGM can be referred to morespecifically as a His IEGM. Step 1202 is the same as step 502 describedabove with reference to FIG. 5 , and thus, additional details of step1202 can be appreciated from the above discussion of step 502. Stillreferring to FIG. 12 step 1204 involves, for each of a plurality ofcardiac cycles during which the IEGM is obtained, sensing or pacing aright atrium of the patient to thereby sense or pace an atrial event.Step 1206 involves, pacing the patient's His bundle at a shortened AVDfollowing the sensed or paced atrial event. Step 1208 involvesdetermining whether a portion of the IEGM exceeds a specified sensethreshold within a specified window that begins the shortened AVDfollowing the sensed or paced atrial event.

Step 1210 is a decision block or step, which directs flow to step 1212or to step 1214, depending upon the results of step 1208. Morespecifically, at step 1210 there is a determination of whether or notthere was a determination (at step 1208) that a portion of the His IEGMexceeded the specified sense threshold within the specified window. Ifthe answer to the determination at step 1210 is No, then flow goes tostep 1212 and it is concluded that AV node capture occurred. However, ifthe answer to the determination at step 1210 is Yes, then flow goes tostep 1214. While steps 1208 and 1210 are shown as two distinct steps inFIG. 12 , these steps can alternatively be combined into a single step,as would be appreciated by one skilled in the art.

Step 1214 involves pacing the patient's His bundle while graduallydecrementing the His bundle cycle length pacing interval. In otherwords, at step 1214 the interval from one HBP pulse to the next isgradually decremented over time.

Step 1216 involves determining whether a Wenchebach type response isdetected (in response to pacing the patient's His bundle while graduallydecrementing the His bundle cycle length pacing interval, at step 1214).Step 1218 is a decision block or step, which directs flow to step 1220or to step 1222, depending upon the results of step 1216. Morespecifically, at step 1218 there is a determination of whether or notthere was a determination (at step 1216) that the Wenchebach typeresponse was detected. If the answer to the determination at step 1218is No, then flow goes to step 1220 and it is concluded that His bundlecapture occurred without AV node capture. However, if the answer to thedetermination at step 1218 is Yes, then flow goes to step 1222, and itis concluded that AV node capture occurred. While steps 1216 and 1218are shown as two distinct steps in FIG. 12 , these steps canalternatively be combined into a single step, as would be appreciated byone skilled in the art.

The Wenchebach type response (which is related to the WenchebachPhenomenon) can be detected by determining whether stimulation-to-onset(stim-to-onset) intervals progressively increased in response to thegradually decrementing over time the His bundle cycle length pacinginterval. The Wenchebach type response (which is indicative of AV nodecapture) is detected if it is determined that the stimulation-to-onsetintervals progressively increased in response to the graduallydecrementing over time the His bundle cycle length pacing interval.Conversely, the Wenchebach type response is not detected if thestimulation-to-onset intervals remain consistent (i.e., substantiallythe same length) in response to the gradually decrementing over time theHis bundle cycle length pacing interval.

In accordance with certain embodiments, the AV node capture testdescribed with reference to FIG. 12 is performed when the system/deviceis in DDD mode, and HBP is performing using a paced/sensed AVD of 50/25ms (i.e., 50 ms following an AP, or 25 ms following an AS). During suchHBP the amplitude of the HBP pulses should be sufficiently high toensure His capture. Further, in certain embodiments, the stim-onsetintervals are measured withing search windows of 140 ms from His pacing.If no evoked response is detected for any of the beats, the test woulddeclare AV node capture. Otherwise, if every beat has a stim-onsetinterval of less than 140 ms, a decremental cycle length pacing testwill be performed to check for the Wenckebach phenomenon, which isunique to the AV node. In the case of AV node capture, the stim-onsetinterval would progressively prolong with decreasing pacing cycle lengthtill eventually loss of capture occurs. Whereas in the case of Hiscapture (without AV node capture), the stim-onset interval would remainconsistent till loss of capture of the His bundle occurs when the pacingcycle length reaches the His effective refractory period.

FIGS. 13A and 13B are used to show two different possible responses thatmay occur in response to the pacing performed at step 1214, i.e., topacing the patient's His bundle while gradually decrementing the Hisbundle cycle length pacing interval. In FIG. 13A the His bundle cyclelength pacing intervals are shown as being decreased from 600 ms, to 500ms, to 400 ms, to 300 ms, and the respective stim-to-onset intervals areshown as increasing from 100 ms, to 120 ms, to 140 ms, to 160 ms, whichcorresponds to a Wenchebach type response. Accordingly, if the responseshown in FIG. 13A were detected in response to the His bundle cyclelength pacing intervals being gradually decreased, then the AV capturenode test would conclude the AV node capture occurred.

In FIG. 13B the His bundle cycle length pacing intervals are again shownas being decreased from 600 ms, to 500 ms, to 400 ms, to 300 ms.However, in contrast to FIG. 13A, in FIG. 13B the respectivestim-to-onset intervals are shown as remaining consistently at 100 ms,which does not correspond to a Wenchebach type response. Accordingly, ifthe response shown in FIG. 13B were detected in response to the Hisbundle cycle length pacing intervals being gradually decreased, then theAV node capture test would conclude the His bundle capture occurredwithout AV node capture.

It is to be understood that the subject matter described herein is notlimited in its application to the details of construction and thearrangement of components set forth in the description herein orillustrated in the drawings hereof. The subject matter described hereinis capable of other embodiments and of being practiced or of beingcarried out in various ways. Also, it is to be understood that thephraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Further, it is noted that the term “basedon” as used herein, unless stated otherwise, should be interpreted asmeaning based at least in part on, meaning there can be one or moreadditional factors upon which a decision or the like is made. Forexample, if a decision is based on the results of a comparison, thatdecision can also be based on one or more other factors in addition tobeing based on results of the comparison.

Embodiments of the present technology have been described above with theaid of functional building blocks illustrating the performance ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have often been defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed. Any such alternate boundaries are thus withinthe scope and spirit of the claimed embodiments. For example, it wouldbe possible to combine or separate some of the steps shown in variousflow diagrams shown in FIGS. 5,7, 10 and/or 12 . For another example, itis possible to change the boundaries of some of the blocks shown in FIG.3 .

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the embodiments ofthe present technology without departing from its scope. While thedimensions, types of materials and coatings described herein areintended to define the parameters of the embodiments of the presenttechnology, they are by no means limiting and are exemplary embodiments.Many other embodiments will be apparent to those of skill in the artupon reviewing the above description. The scope of the embodiments ofthe present technology should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled. In the appended claims, the terms“including” and “in which” are used as the plain-English equivalents ofthe respective terms “comprising” and “wherein.” Moreover, in thefollowing claims, the terms “first,” “second,” and “third,” etc. areused merely as labels, and are not intended to impose numericalrequirements on their objects. Further, the limitations of the followingclaims are not written in means—plus-function format and are notintended to be interpreted based on 35 U.S.C. § 112(f), unless and untilsuch claim limitations expressly use the phrase “means for” followed bya statement of function void of further structure.

What is claimed is:
 1. A method for performing an atrial capture testthat can be used to detect if and/or when atrial capture occurs inresponse to pacing a patient's His bundle using at least one electrodethat is implanted in or proximate to the patient's His bundle, themethod comprising: during a plurality of cardiac cycles during whichpacing of the patient's His bundle occurs using the at least oneelectrode implanted in or proximate to the patient's His bundle,gradually decremented over time amplitudes of pacing pulses that aredelivered to the patient's His bundle until loss of His or rightventricular (RV) myocardium capture occurs, such that the patient's Hisbundle is paced at a plurality of different pacing pulse amplitudes; foreach pacing pulse amplitude, of the different pacing pulse amplitudesused during the pacing of the patient's His bundle, determining arespective stimulation-to-atrial sense (stim-to-AS) intervalcorresponding to a length of time between when a said His pacing pulsehaving the pacing pulse amplitude is delivered and when a respectiveatrial sensed event occurs; detecting how many increases to thestim-to-AS interval occurred, if any, in response to the pacing pulseamplitudes being gradually decremented over time until the loss of Hisor RV myocardium capture occurs; determining whether atrial captureoccurred, during the pacing of the patient's His bundle, based onresults of the detecting how many increases to the stim-to-AS intervaloccurred, if any; after determining that the atrial capture occurred,determining an atrial capture threshold at which pacing of the patient'sHis bundle will cause atrial capture; selecting a pacing pulseamplitude, at which to perform further pacing of the patient's Hisbundle, that is above an amplitude at which loss of His or RV myocardiumcapture occurs and is below the atrial capture threshold at which pacingof the patient's His bundle will cause atrial capture; and performingthe further pacing of the patient's His bundle at the selected pacingpulse amplitude.
 2. The method of claim 1, further comprising: inresponse to one or more increases to the stim-to-AS interval beingdetected, also identifying a corresponding pacing pulse amplitude atwhich each of the one or more increases to the stim-to-AS intervaloccurred; and wherein the determining whether atrial capture occurred isalso based on the corresponding pacing pulse amplitude at which at leastone of the one or more increases to the stim-to-AS interval occurred. 3.The method of claim 1, wherein the determining whether atrial captureoccurred comprises: determining that atrial capture occurred, if therewere zero detected increases to the stim-to-AS interval in response tothe pacing pulse amplitudes being gradually decremented over time untilthe loss of His or RV myocardium capture occurs.
 4. The method of claim1, wherein: the pacing of the patient's His bundle can result in one ofnon-selective (NS) His bundle capture, selective (S) His bundle capture,or myocardium-only (Myo) capture; depending upon which type of Hisbundle capture occurs responsive to the pacing of the patient's Hisbundle, the loss of His or RV myocardium capture (LOC) that occursresponsive to the gradually decrementing of the amplitudes of the pacingpulses delivered to the patient's His bundle, can be one of selectiveHis bundle capture to LOC (S-LOC), non-selective His bundle capture toLOC (NS-LOC), myocardium-only capture to LOC (Myo-LOC), non-selectiveHis bundle capture to selective His bundle capture to LOC (NS-S-LOC), ornon-selective His bundle capture to myocardium-only capture to LOC(NS-Myo-LOC); and when the patient has one of the S-LOC, the NS-LOC, theMyo-LOC, or the NS-S-LOC, the determining whether atrial captureoccurred comprises determining that no atrial capture occurred if therewas only one detected increase to the stim-to-AS interval in response tothe pacing pulse amplitudes being gradually decremented over time untilthe loss of His or RV myocardium capture occurs; and determining thatatrial capture occurred if there were only two detected increases to thestim-to-AS interval in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs; when the patient has the NS-Myo-LOC, the determiningwhether atrial capture occurred comprises determining that atrialcapture occurred if there was only one detected increase to thestim-to-AS interval in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs; determining that atrial capture occurred if there wereonly two detected increases to the stim-to-AS interval, in response tothe pacing pulse amplitudes being gradually decremented over time untilthe loss of His or RV myocardium capture occurs, and at least one of thetwo detected increases to the stim-to-AS interval did not coincide witha NS capture threshold or a Myo capture threshold; determining thatatrial capture did not occur if there were only two detected increasesto the stim-to-AS interval, in response to the pacing pulse amplitudesbeing gradually decremented over time until the loss of His or RVmyocardium capture occurs, and the two detected increases to thestim-to-AS interval coincided with the NS capture threshold and the Myocapture threshold; and determining that atrial capture occurred if therewas only three detected increases to the stim-to-AS interval in responseto the pacing pulse amplitudes being gradually decremented over timeuntil the loss of His or RV myocardium capture occurs.
 5. The method ofclaim 1, wherein the method is used during an implant procedure to helpselect a location for chronic implant of a lead and/or the at least oneelectrode that is to be used for pacing of the patient's His bundle. 6.A medical system, comprising: one or more implantable electrodes thatcan be used for sensing and pacing; a sensing circuit configured tosense a His intracardiac electrogram (IEGM) using at least one of theone or more implantable electrodes configured to be implanted in orproximate to a patient's His bundle; a pulse generator configured toselectively produce pacing pulses that are delivered to the patient'sHis bundle using at least one of the one or more implantable electrodesconfigured to be implanted in or proximate to the patient's His bundle;and a controller configured to cause gradual decrementing over time ofamplitudes of the pacing pulses that are delivered to the patient's Hisbundle until loss of His or right ventricular (RV) myocardium captureoccurs, such that the patient's His bundle is paced at a plurality ofdifferent pacing pulse amplitudes; for each pacing pulse amplitude, ofthe different pacing pulse amplitudes used during the pacing of thepatient's His bundle, determine a respective stimulation-to-atrial sense(stim-to-AS) interval corresponding to a length of time between when asaid His pacing pulse having the pacing pulse amplitude is delivered andwhen a respective atrial sensed event occurs; detect how many increasesto the stim-to-AS interval occurred, if any, in response to the pacingpulse amplitudes being gradually decremented over time until the loss ofHis or RV myocardium capture occurs; determine whether atrial captureoccurred, during the pacing of the patient's His bundle, based onresults of the detecting how many increases to the stim-to-AS intervaloccurred, if any; after determining that the atrial capture occurred,determine an atrial capture threshold at which pacing of the patient'sHis bundle will cause atrial capture; select a pacing pulse amplitude,at which to perform further pacing of the patient's His bundle, that isabove an amplitude at which loss of His or RV myocardium capture occursand is below the atrial capture threshold at which pacing of thepatient's His bundle will cause atrial capture; and cause the furtherpacing of the patient's His bundle at the selected pacing pulseamplitude.
 7. The system of claim 6, wherein the controller is alsoconfigured to: identify a corresponding pacing pulse amplitude at whicheach of one or more increases to the stim-to-AS interval occurred, ifthe one or more increases to the stim-to-AS interval are detected; anddetermine whether the atrial capture occurred, during the pacing of thepatient's His bundle, also based on the corresponding pacing pulseamplitude at which at least one of the one or more increases to thestim-to-AS interval occurred.
 8. The system of claim 6, wherein: pacingof the patient's His bundle can result in one of non-selective (NS) Hisbundle capture, selective (S) His bundle capture, or myocardium-only(Myo) capture; depending upon which type of His bundle capture occursresponsive to pacing of the patient's His bundle, the loss of His or RVmyocardium capture (LOC) that occurs responsive to the graduallydecrementing of the amplitudes of pacing pulses delivered to thepatient's His bundle, can be one of selective His bundle capture to LOC(S-LOC), non-selective His bundle capture to LOC (NS-LOC),myocardium-only capture to LOC (Myo-LOC), non-selective His bundlecapture to selective His bundle capture to LOC (NS-S-LOC), ornon-selective His bundle capture to myocardium-only capture to LOC(NS-Myo-LOC); and when the patient has one of the S-LOC, the NS-LOC, theMyo-LOC, or the NS-S-LOC, the controller is configured to determinewhether atrial capture occurred by determining that no atrial captureoccurred if there was only one detected increase to the stim-to-ASinterval in response to the pacing pulse amplitudes being graduallydecremented over time until the loss of His or RV myocardium captureoccurs; and determining that atrial capture occurred if there were onlytwo detected increases to the stim-to-AS interval in response to thepacing pulse amplitudes being gradually decremented over time until theloss of His or RV myocardium capture occurs; when the patient has theNS-Myo-LOC, the controller is configured to determine whether atrialcapture occurred by determining that atrial capture occurred if therewas only one detected increase to the stim-to-AS interval in response tothe pacing pulse amplitudes being gradually decremented over time untilthe loss of His or RV myocardium capture occurs; determining that atrialcapture occurred if there were only two detected increases to thestim-to-AS interval, in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs, and at least one of the two detected increases to thestim-to-AS interval did not coincide with a NS capture threshold or aMyo capture threshold; determining that atrial capture did not occur ifthere were only two detected increases to the stim-to-AS interval, inresponse to the pacing pulse amplitudes being gradually decremented overtime until the loss of His or RV myocardium capture occurs, and the twodetected increases to the stim-to-AS interval coincided with the NScapture threshold and the Myo capture threshold; and determining thatatrial capture occurred if there was only three detected increase to thestim-to-AS interval in response to the pacing pulse amplitudes beinggradually decremented over time until the loss of His or RV myocardiumcapture occurs.